I had heard about that and so I had one of my sims get two roommates to see if it would happen, but I never got that message, which is odd because it was 3 sims living in that little Crick Cabana house in Willow Creek with only one bathroom and not great beds. For the most part - the two roommates did stuff - played on the computer, painted, played violin, used the basketball hoop, exercise equipment and water slide, but whenever my sim went to work - they usually would just sit on the couch the whole time he was gone playing with their phones. Roommates do have hidden traits (it was in another post somewhere on the forum) that make them do certain things - like play violin, bring food all the time, be slobs, have parties, etc. I know one of the roommates had the erratic trait - forget the other traits right now. I don't have any mods so not sure if that is the difference.