@Kolyo,
Agreed. Each family is different in how they view it.
I've known a couple of people, one a good friend, who at one point or another, for either a short or long period, moved back into the family home. It worked fine.
Thinking about it, I believe a big part of the success was that no one fell back into the role of dependency or caretaking. There was no "mom or dad will take care of that. The adult son or daughter is not a child. On the other hand, because they aren't a child, there was no policing on the parents part of their comings and goings.
In fact, my good friend, who is my age, now has his 88 year old dad living with him. His mother died some time back. So, it's reversed from son living with parent, to parent living with son.
When he did live at home as an adult, he was past the age of "having a roomate" He had a good job, and financially could have rented or bought. However, it enhanced everyone life style when the 3 of them lived together. As well as contributing to the mortgage etc (he was going to own the home anyway someday) he also paid for a housekeeper to come in once or twice a week. The entire house was spotless, laundry done and put away, fresh linens on all beds, etc.
This afforded everyone more time, a precious commodity, and they also all came home to a clean pleasant home.