> This is where the whole "I looked up nike shoes on Amazon and now I'm getting nike shoe ads on Facebook" comes from. Without the IDFA, Facebook has no way of

> This is where the whole "I looked up nike shoes on Amazon and now I'm getting nike shoe ads on Facebook" comes from. Without the IDFA, Facebook has no way of knowing what you looked up on Amazon, only what you look up on Facebook. That's not really true, as far as I know. FB provide a feature called custom audiences, which can take a set of emails and match them to FB users. Amazon could easily upload this list and use it to target on FB. Apple can't really prevent advertisers/platforms from sharing information from other sources. What they can stop is apps using IDFA as a primary key for a particular Apple user, and that's what they appear to have done.