I'm not sure why you'd think it's not useful to someone somewhere.
Game devs see how much time you play games, what type of games, if you purchase IAPs, etc. News feed apps sell what kind of news stories you read/follow/subscribe. Commerce apps sell what kind of things you buy, the prices you pay, the items you look at but don't buy etc.
From all of that "metadata", one can build up a profile about you that's pretty accurate. If you can't imagine why that is useful to someone, then I'd posit you're not trying hard enough.
Game devs see how much time you play games, what type of games, if you purchase IAPs, etc. News feed apps sell what kind of news stories you read/follow/subscribe. Commerce apps sell what kind of things you buy, the prices you pay, the items you look at but don't buy etc.
From all of that "metadata", one can build up a profile about you that's pretty accurate. If you can't imagine why that is useful to someone, then I'd posit you're not trying hard enough.