Kids do tend to take a little better care of things *their* money goes to, huh?
Not only that, but they don't feel like you're holding the fact that you paid for it over their heads. That can go a long way to making adolescence go by much easier. It's not necessarily that you'll do so, but more the perception on the part of the child. I'm very glad that with my first car, my parents fronted the money, but I slowly paid them back all the money (no interest) by working. It made me feel like they couldn't hold it over my head, even though they didn't.
With the way an adolescent thinks and/or rationalizes during an argument, this can be a Big Deal.