One of the most important end goals of parenting is to give your kids the tools they need to function in the world on their own. Adult children should not have to rely on their mom and dad to help them make every decision, and that won't happen unless parents give their kids room to make mistakes when they're teenagers.
While all that is true, nothing says that adult children must be wholly independent of their parents once they reach adulthood. Being a young adult can be lonely, and there's nothing wrong with spending a lot of time with your parents. Contrary to popular belief, parents don't stop being parents the second their kids are responsible enough to pay their own rent and technically function without them. Just because you can live without your parents doesn't mean that you should. One woman in her late twenties recently went viral for going through her commute with her parents, and while some people think it's a little age-inappropriate, many others have stepped in to defend her.