I started living with S and K (along with a couple other people not in the relationship) almost before I had started dating S or knew what poly was. It all happened so quickly I can't remember what happened first.
One issue that arose (and we are still work through) is that interior walls are not usually well insulated. Being new to poly (and still not sure I am poly) it was highly stressful to hear S and K in the next room. Even laying alone trying to sleep while S was less than 15ft away gave me a fair bit of trouble. For many people this is probably a non-issue but it is a potential one that I haven't seen brought up yet. It is one thing to know your partner is out on a date in a mystical "out there". It is something else entirely to know your partner is with someone else a couple of rooms over. S, K and, I have all had to work on being conscious of how much noise we make in bed