I've had my 5 squads training in a couple barracks for many years now. No issues.
They sleep in the barracks and get a couple months off a year where they can sleep where they want, and do what they want.
They're close to the dining hall, food, meeting place, and rooms.
I decided to make a a secondary entrance to the fort a few levels up. It's actually attached to a giant courtyard which holds my windmills. Walled in. There is a lot of wood up there so I built a small secondary area up there. a couple stockpiles, a tiny dining room (not a meeting spot), a small food stockpile, a small dormitory, in case anyone was working there and needed to sleep.
I've got two dwarfs from the same squad. I found both of them sleeping on the floor in that dormitory. Not even on the beds. They just wandered all the way across the fort to sleep on the floor. I made sure that that area was not as nice as the area they're in. Their area is engraved, this area is smoothed only. They are currently on schedule. They are not on break, their schedule shows them training in the current month. His thoughts even reference that he admired his own fine bed recently..
1. They have no business being up there. They're not assigned to that dormitory, and as far as I know they've claimed their own rooms long ago anyway
2. they're on schedule and set to sleep in the barracks
3. it's been months since I've ordered them to do anything so they weren't in this area for a recent order
4. all labours are turned off, so nothing would have taken them up there.
5. There is no bed shortage in the barracks, even if there was I'd expect him to go to his room, not some random dormitory half-way across the map and several z-levels up.
There is absolutely nothing they could want up there that they couldn't get much closer and in a better environment.