on Non Fiction Authors Association:
When you self-publish a book, you have several options for launching it into the world. You can host a presale on Amazon and promote it for weeks or even months in advance. This strategy can be effective, especially if you have a following of supporters and want to build sales momentum.
You can also decide to launch your book and hit the ground running, though this strategy can backfire if you promote the book on the same day it’s released and you haven’t yet worked out any kinks. Amazon can be glitchy and a bit frustrating, so your book may not be ready for prime time (no pun intended) right out of the gate.
I prefer to use a Soft Launch strategy for newly published books, which can be surprisingly simple and effective.