Theory on reasons for there to be non-automated systems on a spacecraft, to get that sweet sweet drama providing crew on board.
Mostly, the nitch I think would come if theres a sweet spot where having a manual system becomes either cheaper or lighter than automation, with lighter being the more significant.
For example, lets compare a very simple automation question: dish washing. This is of course assumes some sort of artificial gravity/long term journey, but lets stick with it. Lets say having that automated adds an extra 100 kg of weight, compared to doing so manually. Obviously, that's no saving compared to an additional crewman there if they just washed dishes by hand, since he likely weighs close to that by himself and has a lot of extra mass to support him.
However, there are from my understanding significant returns to scale as you enlarge the ship, so that per crewman mass penalties go down as you get a larger crew.
For example, lets say each crewman needed 25 cubic meters of space per person. For a crew of 10, you need 250 cubic meters. If the pressurized part of the hull was a sphere, that would be a sphere roughly 8 meters wide, with a surface area of 191 m^2. If the walls were 10 mm aluminum, each meter of wall would weigh about 30 kg. So, the entire pressure vessel would weigh about 6 tons, (rounding up), or about 600 kg of wall per crew member. Ouch. Making things a bit more cosey, or cutting a crew member, would save a lot of weight: going for a crew of 9, assuming the same needed internal space, cuts down the pressure hull's weight by about 600 kg. That's a lot of weight saving on pressure hull alone, and can allow for a lot weighty automation equipment to be stored and still have a mass savings.
If you had a crew of a 100 however, with the same 25 meters per person requirement, you need a sphere 16 meters in diameter, with a surface area of 890. This suggests the pressure wall will weigh about 27 tons, or about 270 kg per person. Still significant, true, but much less of a burden. And, with more space, it may be more possible to specialize the available space to reduce per crew needs. If you had a 200 man crew, the pressure vessel's weight only goes up to 42 tons, and per crew weight is reduced to 212 kg.
Of course, hull weight is not the only support people need, but its my understanding a lot of those supports have even more dramatic drop offs/returns to scale: for example, its a huge cost when your crew gets large enough to need a dedicated kitchen area, but once you have a proper kitchen, that kitchen can take care of more crew at fairly trivial increases in kitchen specific consumption: a kitchen to feed 200 is not much bigger than what you need for 100.
Still, having more crew making supporting each crew less expensive doesn't justify having all the crew in the first place, or using crew instead of automation. For that, I think the key to justification has to be multi-purpose.
To return to the dishwasher example, lets say all in the crewman takes up 1 ton of support structure, vs the dishwasher requiring 100 kg. In mass savings, that's a 10-1 mass savings, and the dishwasher can likely wash more dishes in a shorter time to boot. In dishwashing, the automation clearly wins out. However, "dishwashing" involves more than washing the dishes: you have to feed the dishwasher, put the dishes away, and other tasks. There's a reason despite the widespread use of washing machines you still need dedicated dishwashers in most jobs. So, a dishwashing system that fully automates the process is likely going to be significantly more than 100 kg. Which is going to cut into the mass benefit significantly. Then lets say the crews not big enough to use the dishwasher 24/7. If you have the dishwasher, its dead weight when not in use. However, if the crew could complete the dishwashing job in 4 hours of daily work, then they can do another 4 hours of work, say cleaning, removing the need for an automated system for that. And can then carry things between parts of the ship, removing the need for an automated system for that.
Thus, while the crew doesn't win out on weight for any one automation task, they win out when there are a large number of tasks that need to be done.
This is even more so in situations where you need the people anyways. The most obvious situation for this is colony ships: if you have a lot of people paying for passage, if you can remove machines who are not paying their way with more colonists who are paying their way and make them do some work to pay their way, that's probably better for making the colony ship cheaper. So, colony ships may be surprisingly light on automation, due to having a potentially large population of captive workers who are otherwise skilled.
Warships may be less automated than expected, depending on what the ratio of people necessary for combat vs normal operation is. So, for example, combat needs a 100 people available for damage control, system operations, excetera: if a 100 people is the necessary number for those couple of hours/days in combat, then, adding extra weight/mass in automation systems when you have otherwise idle hands.
Mostly, the nitch I think would come if theres a sweet spot where having a manual system becomes either cheaper or lighter than automation, with lighter being the more significant.
For example, lets compare a very simple automation question: dish washing. This is of course assumes some sort of artificial gravity/long term journey, but lets stick with it. Lets say having that automated adds an extra 100 kg of weight, compared to doing so manually. Obviously, that's no saving compared to an additional crewman there if they just washed dishes by hand, since he likely weighs close to that by himself and has a lot of extra mass to support him.
However, there are from my understanding significant returns to scale as you enlarge the ship, so that per crewman mass penalties go down as you get a larger crew.
For example, lets say each crewman needed 25 cubic meters of space per person. For a crew of 10, you need 250 cubic meters. If the pressurized part of the hull was a sphere, that would be a sphere roughly 8 meters wide, with a surface area of 191 m^2. If the walls were 10 mm aluminum, each meter of wall would weigh about 30 kg. So, the entire pressure vessel would weigh about 6 tons, (rounding up), or about 600 kg of wall per crew member. Ouch. Making things a bit more cosey, or cutting a crew member, would save a lot of weight: going for a crew of 9, assuming the same needed internal space, cuts down the pressure hull's weight by about 600 kg. That's a lot of weight saving on pressure hull alone, and can allow for a lot weighty automation equipment to be stored and still have a mass savings.
If you had a crew of a 100 however, with the same 25 meters per person requirement, you need a sphere 16 meters in diameter, with a surface area of 890. This suggests the pressure wall will weigh about 27 tons, or about 270 kg per person. Still significant, true, but much less of a burden. And, with more space, it may be more possible to specialize the available space to reduce per crew needs. If you had a 200 man crew, the pressure vessel's weight only goes up to 42 tons, and per crew weight is reduced to 212 kg.
Of course, hull weight is not the only support people need, but its my understanding a lot of those supports have even more dramatic drop offs/returns to scale: for example, its a huge cost when your crew gets large enough to need a dedicated kitchen area, but once you have a proper kitchen, that kitchen can take care of more crew at fairly trivial increases in kitchen specific consumption: a kitchen to feed 200 is not much bigger than what you need for 100.
Still, having more crew making supporting each crew less expensive doesn't justify having all the crew in the first place, or using crew instead of automation. For that, I think the key to justification has to be multi-purpose.
To return to the dishwasher example, lets say all in the crewman takes up 1 ton of support structure, vs the dishwasher requiring 100 kg. In mass savings, that's a 10-1 mass savings, and the dishwasher can likely wash more dishes in a shorter time to boot. In dishwashing, the automation clearly wins out. However, "dishwashing" involves more than washing the dishes: you have to feed the dishwasher, put the dishes away, and other tasks. There's a reason despite the widespread use of washing machines you still need dedicated dishwashers in most jobs. So, a dishwashing system that fully automates the process is likely going to be significantly more than 100 kg. Which is going to cut into the mass benefit significantly. Then lets say the crews not big enough to use the dishwasher 24/7. If you have the dishwasher, its dead weight when not in use. However, if the crew could complete the dishwashing job in 4 hours of daily work, then they can do another 4 hours of work, say cleaning, removing the need for an automated system for that. And can then carry things between parts of the ship, removing the need for an automated system for that.
Thus, while the crew doesn't win out on weight for any one automation task, they win out when there are a large number of tasks that need to be done.
This is even more so in situations where you need the people anyways. The most obvious situation for this is colony ships: if you have a lot of people paying for passage, if you can remove machines who are not paying their way with more colonists who are paying their way and make them do some work to pay their way, that's probably better for making the colony ship cheaper. So, colony ships may be surprisingly light on automation, due to having a potentially large population of captive workers who are otherwise skilled.
Warships may be less automated than expected, depending on what the ratio of people necessary for combat vs normal operation is. So, for example, combat needs a 100 people available for damage control, system operations, excetera: if a 100 people is the necessary number for those couple of hours/days in combat, then, adding extra weight/mass in automation systems when you have otherwise idle hands.