So, yeah. It's hard to see the "so what" on the end of that, and why you should care.
Lemme give you an example:
Police have been getting a list of all the cellphones in the area where a crime was committed. They then paw through all these cellphone numbers and get their records from the cellphone companies. Where the phone was (GPS), who the phone called, who the phone texted, who texted the phone, who called the phone, what web sites the phone visited (all that data went over the cellular data network, so is also available), etc.
Then they try to find correlations in all this data. (They have automated tools for this, documented by Snowden and others.) If you work in any downtown area, I guarantee you have been in proximity to a crime. A hit and run. Bank fraud. Drugs. Stalking. Whatever. Someone in your 40-story office building has done something bad. It's just basic statistics.
So let's say that lawyer on the 40th floor is being investigated for buying cocaine. And you are a barista working in the Starbucks on the 1st floor.
The lawyer comes in to your Starbucks every single day for his quad-shot venti latte. So both of your phone record a GPS location right next to each other every single morning, all week.
And since you are a Starbucks barista, and young, with lots of student debt, you don't live in the best part of town. You have four roommates, and live in the "sketchy industrial/artist-friendly" part of town. Also a part of town known to the police for being a hotbed of drugs and illicit activity.
According to the algorithms, you might be the lawyer's drug dealer.
So now the police are tracking YOUR phone...
And you grab an Uber with your friends, and go to a warehouse where there is an underground rave that gets busted by the cops. You got nothing to worry about, right? You are just a barista who went to a party with friends. (Oh, and one of those friends has a restraining order against him by his high-school girlfriend's dad, who didn't like him. So now you are riding with a convicted Bad Guy.)
A barista who talks to the suspicious lawyer every day.
A barista with big student loan payments due every single month. And you have been making the payments on time. (Maybe because your parents are slipping you some cash every month, so it's off the books.)
Now you are paying bills you don't make enough to cover, you frequent "known drug dens", and the lawyer knows you by name.
So the police say, "We got you, drug dealer. Cop this lesser plea of possession, and we'll put you on a six month watchlist. You keep your nose clean, and you'll just get a little black mark on your record. OR, we can go to trial, and it'll cost your parents $150,000 in lawyer fees, and you won't win anyway, because the lawyer copped a deal pointing to you as his supplier, in exchange for keeping his name out of the press."
This happens. All the time. Today. (See: Black people.)
Get it now?