It's been a massive battery drain for me as I have no Google services. It's a known bug. You can't really turn off that drain either in favor of getting messages later.

https://github.com/signalapp/Signal-Android/issues/6898

https://github.com/signalapp/Signal-Android/issues/9194

Other apps like Threema or Telegram might delay messages sometimes, but at least they keep my device operational. If I'm punished for opting out of Google's spying, I at least want to choose the punishment.