From the girls I've been with, they've said it is kind of hard to tell, but the motion seems a little smoother when retacting, they say of course this makes the friction from the thrusts inward have more affect. One said it felt more like she was being fucked by a pitching machine where it just kept coming in. But these were the most extreme of the responses. It's usually pretty comparable and naturally it only comes into play without condoms.