They haven't provided one, but I'm guessing if someone provides a source, it'll be a link to Microsoft's ads products. They'll argue this information _could_ be used to target users for advertisements, even though it might not be.

like this?

https://law.stackexchange.com/a/1848/1059

you're dismissive, but they've specifically claimed the legal right to sell your usage data. it seems pretty clear to me.