Transparency of app tracking is great for iOS users, not so much for advertisers
In other words, Apple asks users if they allow third-party apps to share data such as their age, location, browsing history, spending habits, and health. Some apps with built-in trackers share this data with advertisers and data brokers. This information becomes a digital profile which is sold to others who use the profile to send these users targeted advertisements and to make predictions about how they will react in certain circumstances.

Apple Application Tracking Transparency Feature
As Apple notes, this happened without your permission and made you the product. When ATT was first announced by Apple, Facebook struggled to say it was going to hurt small businesses, as the vast majority of iOS users would likely deny permission to be tracked. And, by the way, Facebook was also worried about its own business, which is as heavily ad-dependent as it is.
As a percentage, Snap lost the most money because its advertising is the most related to smartphones. Marketing consultant Eric Seufert told the Financial Times that “Some of the most affected platforms – but especially Facebook – have to rebuild their machines from scratch as a result of ATT. I think it takes at least a year to building a new infrastructure.. New tools and frameworks must be developed from scratch and thoroughly tested before being deployed to large numbers of users. “
Is Apple using ATT as a smokescreen to hide its own advertising ambitions?
Some also believe that Apple created App Tracking Transparency and its other privacy features in order to grow its own advertising business. One analyst said that ATT could be a smokescreen used to hide Apple’s real desire to create its own search algorithm. On the one hand, Apple’s advertising activity has tripled since it made privacy changes.