The Primm houses, IIRC, are all "owned" - that is, all the containers are marked as owned/have red text - except the mailboxes outside, and all mailboxes do tend to respawn once or twice (so not safe). This means every time you open them and take something out, you get a neg. karma hit. This applies, last I knew, to stuff you put in them, not just the original stuff. So basically, while I don't believe the containers will respawn, every time you fiddle with inventory/remove stuff, your karma will drop. Also, if the townspeople ever return to their homes and see you "stealing", it might be a problem. Not sure about that one, I've never gone back to those houses to see if they start sleeping there once they leave the saloon.
Why do people have houses? whats the point? To store things? You can just give it to your companions or sell it.
Some people dont use companions...some don't even ever hire them. Some like to collect things, because, well, to them it's fun and something to do in the game.