So where does the data gathered go when you opt in to location tracking? A revealing article in Adage:
Location Tracking and the Trouble With 'Opting In' By Kate Kaye
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—to hail a ride, find nearby restaurants or forecast the weather. And then they forget about it. .... 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. And many companies treat consumers' initial "Allow" as a blanket opt-in for a range of later data uses. .... "