The rear and mirror cameras being active is one reason I don't like it when my phone is connected to it because they overlay what Carplay/Android Auto is trying to show. It's sort of like downgrading from dual screen to one.
I've never found it to be inconvenient. When I'm reversing, I'm not using Carplay actively. I guess it could be annoying if you're a passenger trying to key in a destination or something, but I'd just use my phone in that case (or have the driver unlock their phone).
My car has side cameras that activate when the turn signals are active and that is usually precisely at the same time that I need to see directions for a major interchange or similar. I'm guessing it's been fixed but I find mixing the UI of my phone with my car's built in UI can create some unexpected behaviors.