As I rewrite — I mean major, kill-off-characters, change-plot-direction rewrite — the first Demon series book (now entitled The Mark of the Spider), I am struck by how useful it is to write the synopsis as I go along.

Chuck Sambuchino, Writers Digest, 2014
I realize I am including too much background, or backstory, in The Mark of the Spider. Keeping a lot of backstory demonstrates how much I have thought about and researched the background, thus gratifying my ego, but it slows the action.
Not everyone shares my enthusiasm for background, although I’m sure Herman Melville would.
I’m currently stuck at the “muddle in the middle” of the story, and in reviewing the synopsis I realized I have too much thinking going on and not enough action racing along. I need to work out a balance between the two, but I can start work on it now that I understand the need exists.
Lesson learned: Don’t wait until the end to write the synopsis. It can be a handy tool while you write.
Amen! I think of it as a roadmap, not a GPS.