In different parts of your iOS settings, Apple will ask you it it's OK for ads to 'track' you, OK to 'personalise' ads and OK to 'measure ad effectiveness'. Framing is important.
However, I think that “track” sounds much more invasive than personalize. Of course we know they’re the same damn thing, but “personalized” sounds more innocent.
Serving personalized ads is the goal and tracking is the means.
https://webkit.org/blog/11529/introducing-private-click-meas...
From a pure privacy perspective, it's odd because it involves the browser collaborating in measuring the results of your behavior. I think it shares several of the concerns with Google's FLoC and "privacy sandbox" proposals.
It only makes sense if you buy into Apple's perspective that there's a level of "acceptable" tracking, and new tracking features under that threshold are acceptable if they give Apple the political capital to kill tracking technology that crosses that threshold. It's a bit much to swallow. But they are at least trying to address that concern.