It's baffling that this information is worth so much. I'm curious as to what marketing is being custom sent to me based on the location data they get from me. I actually leave me phone at home most of the time if I'm going to the store or a nearby restaurant but I always take it with me when I go hiking. Even though I turn it off at the trailhead to save the battery in case I need it later, I'm sure I'm identified in…
I have heard it is used by some marketing firms, I have heard that some corporates use it for data on their own properties/competitors (the former may not be obvious, but some malls may do this to check on tenants, malls also usually have their own tracking stuff on site too btw) but the main user are hedge funds.
Not all of this data is useful by itself but it is useful once you integrate it with everything else (lots of firms have tried to use this data on it's own, and then complained it "doesn't work" when they employ no-one who actually understands the restaurant business, for example).
Also, I will say too...99% of this data is coming from free apps whose only purpose is to harvest data from the unwitting. I don't understand fully how this is possible because, presumably, it should be quite obvious to App Stores that a flashlight app does not need to know your location...but it keeps happening. Some of the big data aggregators are actually pretty creepy, I have seen some companies retailing personalised data on every person in the US, I don't think anyone knows where it is all coming from apart from them (I also wouldn't discount hacking tbh, there is so much money in this that I think they have to be doing it).
Imo, all this shit should be blocked. Even within hedge funds, you are seeing funds that are using this data, no-one knows where it comes from, how it was collected, and they making piles of money from it but no-one else can access it...they just call up a firm, tell them they will pay $50m/year if you don't sell this to anyone else, it is all very opaque.