From a while back now, but always relevant: Google apparently uses embedded fonts to track iOS users.
It’s worth noting this also applies to Google’s webfonts (what, you thought they were offering them free out of a burning love of webdesign?).
(Disclaimer: I still use Google Fonts quite extensively because, well. It is just easier than the alternatives; modern browsers can make embedding fonts actually pretty difficult. But yeah Google’s library is definitely A Tracking Thing.)