[benoliver999]

In my experience it's not bad enough to worry about.

I have:

- Signal - Whatsapp - Etesync - Conversations.im - Syncthing

all whitelisted from battery optimisation, and I've not noticed any huge drain (I expected it to be unusable and have to go back to google play services or micro-g).

[jjeaff]

Signal uses gcm to push to the phone thus waking it so it can download any messages. Not sure about the others though.

[zuron7]

If you don't have Google Play Services, it doesn't use GCM.