[nimrody]

Do you use whatsapp or any similar messenger app? If so, do you receive notifications when the app is not running (foreground or background)

Play services is responsible for connectivity with Google's servers which are used to distribute notifications to the device.

Play services is probably also responsible for backing up the App's data to Google servers (not sure about this one)

[ViViDboarder]

Those aren't first party apps.