In six months, the only thing we learned: half of the users that finish setting up don't continue to use the app. We could have learned that from server side logs without invading user privacy.
Another story: four employees of a large corporate running target marketing based on behaviour of customers logged in to their website.
Added revenue versus control: 60.000 yearly. Sub-0.1% conversation rates. The corp had been running these campaigns for at least five years.
My personal stories. Anecdata, I know.
There is SO MUCH BULLSHIT.
Edit: to clarify the first example, it's not a movie using the front facing camera, 'just' a screen grab