My mother didn't charge me rent. I was expected to contribute to shared costs as I could. She wasn't well off and was on benefits, but owned a house so at least no rent/mortgage.
Because she didn't charge me rent, I was able to save up for my own house deposit whilst working.
I met my partner whose parents had done the same, and when things got serious and had half a deposit each, and was able to buy a house.
I know many of my friends who were charged rent by parents or left to rent their own places, who now fear they will never be able to buy.
For all my mothers faults, she did me an absolute solid here.
I don't blame parents who literally cannot afford the cost of another person living in the house without them paying - they lose benefits, for example, and council tax may increase. Times are hard.
But those parents who don't need to charge, I do wonder why they have to do their kids so dirty just "because lesson". What lesson? That you're a dick? There are better ways to teach young adults life lessons that arnt totally screwing them over for profit.