Those are very good points! Thank you.
Initially, I didn't have or want any prologue, but I kept getting feedback of people wanting more and more of the backstory. So I finally caved and instead of telling them bits and pieces, I showed them, tossed them in the scene. The feedback I got was...
Sometimes I do it with the intent of writing a series. But with the one I'm working on now, for example, I was determined to make it one story! And when I realized that wasn't working, I re-worked the plot and found that it's going to have to be a trilogy or else I risk rushing it.
I'm writing a trilogy. The first book has a prologue which tells the backstory from hundreds of years ago. I'm thinking of adding prologues in the other two books where it tells a fuller backstory. The purpose will be to hint at what the rest of the book is about, essentially filling in gaps...