There is a whole bunch of data Microsoft starts to collect from your usage, storing, using it, and selling it.

A simple search with a search engine that also spies:
https://www.google.de/webhp?sourceid=chrome-instant&ion=1&espv=2&ie=UTF-8#q=windows+10+shares+password
results in a lot of articles how to avoid Microsoft's data mining for the most part.


Desktop; i7-2600k, 8 GB mem., Win 10 Pro, BIAB 2017; RB 2017 - latest build
Laptop: i5-2410M, 4 GB mem, Win 10 Pro, BIAB 2017; RB 2017 - latest build