If Apple were interested in using (or selling) your data for advertising they would have done it long ago.
I would imagine that Apple is indeed looking at the long game with their face-tracking technology, not for advertising but for Siri to learn and react to facial expressions. This could potentially give them a huge leap ahead in the personal assistant space.
I would imagine that Apple is indeed looking at the long game with their face-tracking technology, not for advertising but for Siri to learn and react to facial expressions. This could potentially give them a huge leap ahead in the personal assistant space.