The state save is important in terms of being able to rebuild the UI quickly. It's not important in the context of "heavy" resources like files, sockets, etc...

The state save is important in terms of being able to rebuild the UI quickly. It's not important in the context of "heavy" resources like files, sockets, etc... None of those are ever cleaned up in onPause. The worst thing that will happen if you SIGKILL an Android app without calling onPause first is that the next time it's launched it won't resume from where you left off, it will be as if you rebooted the device. Also to be clear the onPause and SIGKILL are not tied together. You could get an onPause and it be minutes or hours or even days before you get SIGKILL'd, during which you are completely free to keep running code in the background. And depending on how your process was started there might not even have been an Activity to be onPause'd in the first place. Consider an app that started doing work in response to a broadcast or content provider query.