What's the difference between wp_insert_user() and wp_create_user()

Question

I know the former allows additional parameters, so you can more user info, but other then that, why do both exist?

The specific reason I want to know is that wp_insert_user() is happening REALLY slowly. Somewhere between 5 - 10 seconds. I don't remember having this problem in the past, when I was using create_user, so I'm wondering if there's a lot more happening behind the scenes with one as opposed to the other.

Thanks.