I've found a video downplaying placing an ad on Amazon. Why? You don't get that passive money unless you really work at it. I've met other authors who make a living by making Amazon ads for their books. So, I guess if you really work at it, you can increase your visibility and get sales. We all know sales=money.
Anyway, this video makes 5 points about it. To be fair, I'm posting not only this video that I spoke of, but following that I'll post a video by the same person saying the opposite thing. I really enjoy the person who created these. I think he has a lot of insight.