The first link goes into amazing detail on that. In short: all your information concerning location as well as current IP and some other metadata gets send to a basically unknown company with no transparency on how that data is handled.
I highly recommend reading the first, linked post though!
As your perception sounds quite negative I'll try to change your view!
Instead of looking down on people fanatifally following a "celebrity", take pity on them:
https://en.m.wikipedia.org/wiki/Parasocial_interaction
In short: their brain chemistry tricks them into thinking that they are following a friend and have the emotional reactions and interests as we'd hope our real friends do.
I find it really sad to be honest.