Anyone who's opened a new app lately has seen a location- tracking pop-up that reads something like, "Allow app to access this device's location?" Most people tap "Allow" on the assumption that it's necessary for the app to do its thing. In reality, the app might not need location data in order to work. But its business partners do, and so do its partners' partners. In fact, making money off otherwise unnecessary location tracking may be the main reason that the app was developed in the first place.