My D's current favorite school has some strict residential life policies. No weekday guests, period, freshman year. To have a weekend guest you have to attend a workshop (!!?).
She is thinking ahead to when her boyfriend plans to visit her in the fall (we won't go into how statistically he will no longer be her boyfriend by then). I was thinking, even if the dorm policies aren't as they are, having an overnight guest, especially one of the opposite sex, is kind of disrespectful to your roommate (in a standard double room). The room is too small for even two people, they have twin beds so boyfriend would need to sleep on the floor, roommate wouldn't feel comfortable changing or lounging in her own room when he's there.
I don't recall many of us having overnight guests when I was in school, even though I went to a wild and crazy university. How about you?