Outside the realm of fantasy, the Prologue is a perfectly acceptable way to foreshadow, show an unrelated or only partially related event that sets the scene, or otherwise provide a frame for the book to follow.
Inside the realm of fantasy, the Prologue is the source of a veritable firestorm of controversy, with some readers swearing they never read them and writers warning each other that it means an agent will instantly pitch their book; and others simply treating them as a valid storytelling tool.
There's a reason for the grumbling within the fantasy community: in older fiction (and still by newbie writers), the Prologue is often used for worldbuilding, and ends up an excuse for creation myths and other elements that more properly ought to be woven into the story gradually and organically. But it doesn't have to be.
Personally, I don't use Prologues too often, not because I have anything against them, but because I'm not a big fan of chapters, either. Ironically, both my published / forthcoming works use chapters, but I flailed and threw things and regretted it the whole time.
On the other hand, I can't comprehend not reading part of a book just because of its label. I'm a completionist.
Prologues work best when they're used to provide a snapshot of events outside the story, not a summary but a scene that may even seem out of context until later in the main tale. If it belongs in a guidebook ... it's not your prologue.
Word Count this week: 8,942
Poems written: 2 (I am counting poems separately / not inclusively)
Pages edited: 5.5