I agree (though I wouldn't use the words "creepy as fuck" but I get your point), I think it's super important that this technology is available only upon permission by the end user - this is what I've done with Sahha to the best of our ability - relying on native permission handling has been super beneficial.

As for use-cases, there are plenty - and some not as direct as others but particularly within healthcare and life sciences there are plenty of uses around efficacy tracking and making sure interventions and treatments can be delivered appropriately based on objective assessment. The latter use leads into the problem many companies delivering health care interventions have with survey fatigue and subjective data bias.