Every man we've ever met has a soft spot for at least one of their deadbeat friends such that they think it is a good idea to let them "crash for a while." You shouldn't necessarily assume that your roommate's younger cousin who "is getting his shit together this time" and "just needs a couple weeks to figure things out" is going to land on your couch, but it is always a good idea to set friend ground rules.
If you're a light sleeper, it's cool to ask that partying friends be out or chilled out by the early a.m. If they're freeloaders, it's cool to remind your roommate not to let them eat all of the Hot Pockets. And it's OK to say that they can't stay with you, no matter how big of a dick the manager who laid them off at Papa John's may or may not have been.