Launcher on android is just that - an app to launch other apps. Other apps can and do run in the background, without ever being explicitly launched. Think play services, location provider, wifi connection manager, etc. Since google runs its stuff at the highest level - nothing can hide from it. Other apps, like netflix, utilise internal telemetry. Assholes like facebook push the boundaries to the limit and collect literally every input of every sensor to have as much data about your environment as possible.
[Some apps] push the boundaries to the limit and collect literally every input of every sensor to have as much data about your environment as possible.
Apps often still work correctly with about 80-90% of their recievers/services/providers blocked, since they're spyware, which doesn't add functionality to the app.
XPrivacyLua will allow you to lie to apps when they request sensitive data.
Aditionally it will show you timestamps of what it lied about, to which apps, reveiling what they try to collect on you.
I don't have something specific to read, my statement comes from questioning the declared permissions by apps. Why would, say, facebook - an app that, essentially, downloads and uploads content via http, need access to location, gyro, contacts, texts, call history, making calls, microphone, etc? Also, while I can't prove it, as someone who works in computing I can guarantee there are undocumented/buggy/testing APIs and just straight up bugs that companies with enough resources can and do find and abuse. Cambridge analytica has only strengthened my view on this.