I've always been so mixed on CEC. On paper, the concept actually sounds great, but I find that it's an example of a great concept that was just implemented poorly. From what I've read (it has been a while), the issue mostly stems from how there aren't always concrete rules on how to implement it, so you can have two similar devices that act differently or in whatever way the manufacturer decides. It's pretty much the reason why I've been using Harmony remotes for the past few years.
CEC works a bit TOO perfectly in my case. While I have special circumstance in my setup, it sucks you can't really tailor it to your needs.
I've got a 4K Projector and a 4K TV. I also have an Apple TV 4K and the nVidia Shield. I use the Apple TV 4K for all streaming services. I use the nVidia Shield almost strictly for Kodi 4K w/ Atmos. The problem is if you use CEC and try to change between project and TV, it powers off my Pre-Pro, Amps and TV, lol. I can't switch (turn off) the Apple TV 4K while turning on the Shield and 4K Projector. It's a bit of a cluster.
I finally just use an URC MX-990 with Macro buttons to command everything. Takes a bit of programing, but it's the best remote I've ever used. I do like being able to create buttons that say "all this off, all this on" using discrete codes. Thankfully, I think almost all my devices have discrete codes.
Then I use Lutron IR switches that will control my lights and ceiling fan in the room. That is really awesome. So you can customize the light and devices based on if you are watching a movie, TV or just hanging with family/friends. Great stuff.
All that said, I can totally see CEC working with a simple setup. The Apple TV 4k can turn off almost everything when you put it to sleep. It's awesome. But it just doesn't work in my multi-device setup.