To answer the question from above - why make the things that complicated? It’s really much easier: they* know that my friends have my phone number which is pretty often located in a close location to my friend’s ones. Using this, some more metadata and the facebook profiles from the other students they can find out e.g. how old I am, which gender i am, what my hobbies are, etc. without ever having any personal data about me.
So, the point is, that as a “normal” person you pretty much have the decission from 0% (using WhatsApp is enough) to max 50-75% of privacy (e.g. not using a smartphone, as horrible as it sounds).
If I had the choice I’d just join those hacker groups who have their own bunkers and can easily cut off any connection to the outside world
Back to your question, I don’t think if someone says… that I like climbing, am 26 years old and my favourite color is red that someone can really use this information for anything but for advertising, maybe. Luckily it’s not that far yet.
I don’t really think that any one is going to describe me as “a guy who has an electric T-378 Lock on the entrance door and a 24-year old laptop from siemens with a modifyed FreeBSD OS”.**
- I mean everyone who has interest in our data
** none of the descriptions are true, of course