I think the vaseline treatment helps retain length by protecting the ends.
Have you read the vaseline challenge thread? I think the first page or so gives some info about the benefits of vaseline.
I'm reluctantly doing this method for the next week or so. I HATE wearing a bun eveyday but I must admit my ends are sooo soft when I take my bun down. I sometimes use Worlds of Curls activator in place of Vaseline.
You are welcome Caligirl. I used vaseline or carol's daughter healthy hair butter on my ends all winter, they never looked better. I just didn't like the greasiness, but it worked well. Good luck everyone.