[WGH_]

Is it really about light vs. heavy though? I thought it was mostly about multiplexing notifications through a single app (usually through a single connection as well), so only one app has to consume resources constantly, and others might be activated as needed.

[ryukafalz]

It's a little bit of both. You want to only keep one connection open as it minimizes the amount of network activity for e.g. keepalives. You also don't want the app holding that connection open to drain the battery in the process though.