At Celebrate Freedom, our usual policy is to give our community members a roommate--even if there's room for them to have a room by themselves. Why? Because we believe that it's dangerous for a person in the early stages of recovery to isolate himself.
When a person isolates, he is more likely to relapse. Think how much easier it would be to sneak drugs or alcohol into a room if he doesn't have to worry about a roommate watching him. Also, it's easier to relapse if you don't have to interact. By constantly being around others in recovery, you're less likely to be tempted into using. After all, the more people you're around, the more likely that you'll be caught!