Hmm, let's go through this together shall we? (1) For their share of the rent. (2) To augment the cost of utilities. (3) To help with the grocery bill. (4) For security reasons. (5) For companionship.
I mean, why would I want annoying ones? There aren't many people I'm ready to share my personal space with.
Can't say for sure, because I prefer living alone/with girlfriends rather than roommates. And I never shared a room with anyone other than my relatives/girlfriends since my youth when I spent the summer in teenage camp.