In an attempt to de-Google my life, I recently disabled Play Services. Now, my Pixel 2 XL complains every time it can't "phone home."
Google wants to contact Play Services (itself a rootkit) every time you receive a call. You'll see the notification/complaint several seconds before the phone rings.
While driving with Maps, Google attempts to track you each time you enter a destination or cancel one as well as at regular intervals during your drive.
Play Services also tries to track me at random times for no reason when I'm not using the phone.
It tries to track you while listening to voicemail and the notification/complaint stops the voicemail playback every few seconds when it can't.
But perhaps the worst offense is that it tracks you as you scroll through your contacts. God help if you look up a phone number because, every few seconds as you scroll through your contact list, Play Services attempts to report it to Google.
I find this behavior reprehensible and I'm sorely looking forward to getting a Puri.sm or /e/ device.
Just for fun, try it for yourself by disabling the Play Services app and see how often Google is spying on you.
Some of it may not be tracking, but rather eager loading info. Like each time a call comes in I bet they query the spam call database to see if the number is spam so they can show their warning. I really like that feature. It would be good to know what is really "tracking" and what is not.