Google Play services
com.google.android.gms
Removing Google Play Services can cause bootloops. If you use “Find My Device”, you will need to remove it from the "Device admin apps" settings panel to be able to remove this package.
GMS = Google Mobile Services. It is a layer that sits on top of the OS and provides a lot of proprietary Google APIs, giving apps access to various Google Services, such as: “fused”-location (internet and GPS chip), QR Code scanner, 2FA, G-Drive storage, Firebase API, Cloud Messaging, etc.
If you remove it, all the apps relying on it will either:
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detect the lack of Play-Services and refuse to run
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detect the lack of Play-Services but allow you to run (improperly) by dismissing an annoying popup.
Disabling this package will improve battery life a lot.