Imo, the conclusion around "worse marketing efficiency" is a logical extension from how Facebook's ad ecosystem works. That is, Facebook is a behemoth in adver

Imo, the conclusion around "worse marketing efficiency" is a logical extension from how Facebook's ad ecosystem works. That is, Facebook is a behemoth in advertising because of its capabilities to predict which users will convert from an ad unit. By predicting conversion rate accurately, FB empower small businesses to get more conversions out of fewer ad impressions and spend. FB's ability to predict conversion rate is driven by a ML algorithm that takes as inputs: all the user data it tracks via the Facebook Pixel, all the user data it collects through its own domains, and data sent via server API's from advertisers. Apple's tracking change reduces the amount of available user data to its ML algo by a large percentage. As a result, prediction power will decrease. And therefore, marketing efficiency. The actual 20-30% estimate is just that, an estimate. But, directionally, there's no question efficiency will decrease.