I have kept separate flocks and let them free range during the day. In my experience, the different flocks kind of went their own way. Not a lot of fighting, really, but we have enough space for them to be away from each other, too. Generally, if a flock is accustomed to sleeping in a certain coop, they will return to that coop on their own at night. When they get it in their heads where "home" is, it sticks pretty well.
X2, We have multiple coops and let the birds free range. The roos don't really seem to bother each other, even the ones from different coops, they just kind of sort themselves out and go their own way with their girls. They do stick to their original coops pretty well, (when getting new sets of birds, usually put them all in the same coop/run and keep them in there for a week or so before letting them out) though some birds wind up in different coops, or have a couple that just seem to sleep in whatever coop they were closest to when it got dark.... also kind of interesting, which coop they pick to sleep in often has nothing to do with which the girls lay eggs in.