I grew up in a big, rambly house with a couple of extra bedrooms on the third floor (where my bedroom was). My mother’s stated policy when cousins older than I visited with b/g-friends was “I’ll assign separate rooms on the third floor, but I don’t go up there for bedchecks.” Then one year we hosted a big holiday party with lots of out-of-town family, some of whom stayed with us, and there just weren’t enough slots to make it work without having one somewhat-established couple share a room. By the time I got old enough to be coming home for visits, and by the time I had a girlfriend to bring home (now my spouse), the old rule was just a memory.
I think you have to be careful what you wish for. At a certain point, you can never be sure when the music will stop – even whether it has stopped already – and the girlfriend or boyfriend du jour turns out to be someone whose good will you will desperately want to cultivate for the rest of your life. My parents didn’t particularly like my girlfriend, and weren’t as welcoming as they might have been. They regretted that stance literally for the rest of their lives.