Read somewhere a loooong time ago that the reason for that is that some applications were doing stupid stuff like sending packets all the time, essentially having a constant use of the network, just to check for new content. When all applications do that, each on its own clock, the battery doesn't last very long.
Which is a shame because a proper application without FCM and proper implementation is virtually invisible. Keeping a TCP socket open costs nothing, even from an app. But it's always the same: if the consequence is that the battery is bad, then the one that is blamed is Google/Apple, not the app maker.
@delta @lyyn
@rakoo @delta @fell I used Signal on websocket without FCM and had a feeling that battery life is not perfect. I believe Signal spent some effort not to do it the stupid way.