Comment by dangus

“Private browsing” is just private mostly in the sense of your local device, as in, your browsing history and cookies aren’t saved to disk. That still has some use as cookies are more direct tracking than fingerprinting (e.g., keeping you logged in, or a Google analytics script seeing that you’re a logged in Google user with a real identity provided to Google).

“Ask app not to track” turns off Apple’s own device identifier, but doesn’t stop other types of identifiers from existing, as the article described by the way it showed how ad networks make their own device identifiers collected by various apps.