My two 50-something sisters and my 30-something niece live with my Mom. They contribute to the household, have a safe place to get their lives back together, and take care of Mom.
In their case, it works out well for all concerned.
I think you’ve pointed out what’s key: it really depends on the situation and the individuals involved.
It can be a good thing or a bad thing; wise or immature; responsible or irresponsible.
It can be one wonderful way a family is there for each other or a way where people are taken advantage of.