Seems a little excessive don't you think? What if you were simply just walking by the TV in the living room with no intention of playing a game?
Then what does it hurt? Xbox One owners run their TVs, Netflix, etc. through there so it signing you in automatically when it turns on lets you stream shows, play games, run any other apps you might have, etc. Since saying 'Xbox On' is how every member of my family turns the TV on in our living room for any purpose whatsoever (if the living room TV is on, the xbox is on: it turns on the audio receiver as well) then having it sign us in so we don't have to go through extra steps to get into netflix, amazon video, etc. is very helpful. In what circumstance would it be harmful?