I can't seem to find Apple's official wording on it within a few minutes, and I don't trust the shit writing of tech blogs online, but some have written that with the new IFA ad networks "can now see if you actually purchased anything, or downloaded an app."
Somehow, all mentions of this on tech blogs that I could find are completely devoid of links to Apple's official documentation on this.
Wasn't there a period of time where UDID tracking was banned and the IFA had not yet been introduced? Some people were probably hoping that situation was permanent.
They now use an anonymous, temporary, random ID that can be turned off.
How is this not an improvement?