Whenever a few of us are sitting around in real life, and someone sends something to a group chat, all the phones on the table will buzz instantly together (iOS and Android).
And on top of that, battery usage is really low on Android. I use it a TON, and it's never in the top n apps of battery usage. Meanwhile, I can just open Snapchat once, and I lose a few percent.
That’s really a mark of Snapchat’s incompetence rather than Telegram’s adroitness.
I suspected that Signal basically took Over Gapps's role since it's the only app I use with notifications. Google keeps open a single optimized connection and apps go through it instead of having 10 open connections. After deleting Gapps, Signal is the only app keeping open a connection so it basically has the same impact.
But then I installed WhatsApp and Signal+WA both work perfectly without Gapps and with no gigantic battery drain. So I have no idea what black magic is making this work.
I just looked up my battery stats; since the last full charge 32 hours ago Signal has used 1% of the power. I got a few notifications and used the app for a few minutes in this time. WhatsApp's power usage is too low to show up in the stats.
Note that since a while there is also the possibility of using web sockets. But they are an extreme battery drain, and thus google services are quasi-mandatory. Telegram solves this without being a battery drain, possibly at the cost of delivering messages with a delay, but why isn't that my choice.