I think anyone who is working full-time should pay rent/board to contribute to their own upkeep. A student who only has a part-time job then no, I wouldn’t ask them to pay unless genuinely needed. But once you’re in full-time work, you should be supporting yourself with your wages, and part of that includes day-to-day living expenses which would be covered by rent/board. Probably not full market rates, so a young person should still be able to save towards a house deposit etc, but still a contribution to the household. That’s regardless of whether the parents actually need the money or not.
Financially, we are at a point where we wouldn’t need DD to contribute because she doesn’t now. But equally we’re not very well-off, so I have to give serious consideration even to buying a relatively inexpensive item of clothing, for example. It doesn’t sit right with me that all of her wages should be for her discretionary spending while I would be supporting an adult to live, and saying to myself “can I really afford this $40 t-shirt?” (This is hypothetical as not relevant to us yet. Right now she is 15, obviously still in full-time school and doesn’t even have a part-time job yet.)
We are not UK, so obviously don’t have anything like child benefit or UC to lose when she leaves school.
I also think people need to give consideration to the fact that young people are living at home for longer and longer. It’s one thing not charging board of an 18-year-old. But would you be willing to fully support a 30-year-old? Especially when, if the kids are that age, then the parents are more likely to be retired or close to it, so probably have less income than they did when working full-time. What age would you support them up to?