Some of my friends were charged rent. My mother never did. If I lost everything, as long as she was alive and still lived there she'd let me stay. She did this for my brother. Later she told me that the one things she asked him was to have a meal with her once a day. He told her that wasn't happening. She still let him stay. I don't respect the man much though.
I paid 'rent' ie: participated in the family funding of stuff. It felt normal to me. Was only required to participate when I had an income and it was less than what I 'd have to pay living on my own.
It's fair that you wouldn't know details, but he moved back home after being fired in his late 20s. He spent little time looking for a long term job and in addition to housing our mother paid for his food and transportation costs.
I've actually got a cousin who is basically in the same situation and has been that way all her life. Gonna be really interesting when her parents are gone.