I think there are a lot of factors to take into consideration. Are you enabling your child to take your help for granted, or are you actually helping them get on their feet? I am the mother of 4 children. I have had two of the four move back in. One was going to college and had a part time job while the other was not in school but working a full time job. The second one needed some more time to get his priorities in order and learn how to succeed in life.
The first one we didn't charge. He was a full time student with a part time job. He was frugal with his money and didn't do a lot of unnecessary going and buying. He spent a lot of time on college. We felt that as long as we could see the effort he was making for a better life by doing his best in college, we felt we were helping to make his future successful. As a parent, that's what I do.
The second son had a rocky start. He liked spending and couldn't quite get the grasp of not spending all of his paycheck before he got paid again. So, we allowed him to come home, pay rent (minimal), help buy groceries and some utilities just like if he were on his own. We helped set up a budget and also helped him start a savings. By not charging a large amount, he had enough to save so that when he got back out, he had enough for a deposit and first month's rent and utility deposits. He was able to move back out and had a much better understanding of money and how to pace his spending. If he had any more problems, we haven't heard!
Not all children are the same and I believe it has to be decided on an indiviual basis. I am thankful that my parents were able to be there for me. Not all parents can afford to help out and I think there are children that have to manage, and do manage without any help. Perhaps knowing that their parents can't afford to help helps them make better choices.