In my opinion, I think a prologue can be used to explain things that happened before the story you're writing happens. Like if I'm writing a story about a war that recently happened, I could write the prologue about how the war started, etc. Other than that, I don't really see a point with prologue except to explain a couple of about-to-be-unclear-if-not-understood facts that will happen in the story.
Eff prologues! Did you know Hemingway cut the first twenty pages of the Sun Also Rises at F. Scott Fitzgerald's suggestion? He said it would work better as a novel without an introduction. I'm not saying some books don't require that, but that tells you two things. 1. Even great writers go on sometimes. 2. For all those people receiving critiques in the Review Room, remember that legends need them too.
