Someone once explained it to me like this...
You never want to rent part of the place you also own. Its like having a girlfriend that you have invested a lot of time, money, and effort into. You let 3 other guys come over and join in on this relationship. They fuck the dog piss out of her while you have to sit there and watch all the dirty shit that they do to her and then you get to see the aftermath. Then (when their lease is up) they leave and you are left with their destruction and one fucked up vag (or house).
Make sense?