Are roost important

I have 3 chickens and one rooster. At night I put the two hens and the rooster in a smaller cage about like a rabbit cage (4 by 2 foot) and I put one in in another cage about the same dimensions which she only comes out of when supervised because she's picked on by the others. At night when I go out to put them up there usually sitting up on her cage I was wondering if putting roost up in their pen would have any advantages or if it is really necessary. They have roost up in the larger pen that I let them out in the day but they don't use them all that much. Thanks for any help.

Chickens are roosting birds at night so long before they're mature, they need a place to roost.
Do you lock them in the rabbit cages to protect them from predators?
Do they have a coop or hen house they can live in and secure at night?

I have a large pen that they go out in during the day then at night I put them into the smaller pens inside the bigger pen (both of which lock) to keep them safe from predators.

Roosting is natural for chickens

As stated by edenrice, roosting is natural for chickens. Some will naturally find their way to the roost at night and others, you will have to place them on the roost a few times until they do it on their own. I'm new to raising chickens and this question recently came up when I added a few more to the flock, because they refused to flight up at night. It was mostly because the older chickens wouldn't let them on the roost yet. After doing some research and speaking to Bill (the guy who sells me chickens), I came to this conclusion. Depending on your coop set up, you may or may not need to force your chickens to roost. (when I say force, I mean putting them on the roost until they stay and doing it each night until they go up on their own) Bill has a large coop with over 100 birds at any time. His coop is quite large and built on the ground. With that many birds, it doesn't get cold inside the coop very easily. My coop, on the other hand, is 7' x 4' and is raised 3 feet off the ground. Bill doesn't mind if some of his chickens sleep on the ground because it won't cause them any problems. However, if my birds were to sleep on the floor and it froze overnight, it could cause problems with their feet. Especially if the litter on the floor was moist from defecation or anything else. Last night, I read an article on here, which was about a chicken who slept on the floor and now has permanent damage to one foot. If I recall correctly, the temperature was about 14°. If it doesn't get down to freezing temperatures where you're at, then you don't have to worry too much. If it does, an enclosed coop with a roost is necessary.

By the way, if your chickens are picking on another, they may be trying to establish a pecking order. If it's too aggressive, you may need to take measures to show the aggressive one it can't behave like that. If that doesn't work, you may need to get rid of the aggressive chicken or send it to freezer camp.

I hope this helps and if anybody sees anything wrong in what I have said, please let me know.