@cuchaz SA360 and now even GA4). The tagline is "this gets around the requirement of 3rd-party cookies because we *already have* user consent for this data sharing".
This only really works for a user who logs into an account on a website or otherwise provides (at least) an email address.
All the users who don't log in, buy something / convert aren't contributing their data in the same way. This is probably what Firefox are trying to fulfil. Chrome is testing similar.
My devil's advocate...
@cuchaz stance is "unless you provide a way for some type of private / aggregate data, bad actor advertisers are going to ramp up illegal collection of user data".
The counter to this would be "but illegal, so this will result in court cases".
Yes, but also not ernough. We already know that regulators are almost entirely toothless when it comes to fining / prosecuting aberrant advertisers.