[oneplane]

It's also how data collection still works if you personally 'block' it but communicate with others who don't.

Your messages, phone book, pictures you share with others etc. are still 'readable' on the remote end and thus still get collected. And if you connect the dots when you have a large collections your personal data can be reconstructed from that.

If you have persons A, B, C and D in your phone book, but your phone book is 'secret', it doesn't prevent someone from knowing that you know A to D if those still have you listed.