Most young adults fight with their parents, for they say their parents don’t give them enough freedom. So living on their own would be a kind of runaway from this, but on the other side they would be out of the control of their parents and having no control or discipline would lead them to being much more irresponsible.
Living alone would teach them to handle life on their own, since they would start thinking in a much more sensible and responsible way of living. They would learn how to deal with the problems of running a house; cleaning, cooking, decorating the house, paying bills etc. But still this would only happen if they were used to keeping everything tidy and neat, since there are young adults who don’t mind living in a dirty place and never clean up or do the dishes.
To conclude, since when they are born people know they can count on their parents any time, so they always take this for granted, not thinking that someday they will have to live on their own and how much depending for everything on their parents can affect their future life. But even though they become responsible and don’t depend on their parents for everything, still they cannot be completely independent. Hence, living alone might be a good way for young adults to learn about real responsibility and life, though they will always depend on their parents some way or another.