What changes in the new feature
The new feature makes a big change when it comes to app developers tracking user data to sell it to advertisers. Before iOS 14.5, developers could use a number of tools to track user data from an app and sell those data to advertisers who would then use that data to create a user profile to target advertisements towards a specific user. It created a chain, as the advertisers, in turn, could sell those advertising opportunities to other businesses to focus on specific user or market segments.
It was not like users had no choice when it came to tracking their data before iOS 14.5. Users could still stop an app from tracking their data. But what the new 'App Tracking Transparency' feature does, is that it puts the choice up front, and forces the developers to give users a very specific choice before even launching the app.
After users update to iOS 14.5, the first time they launch an app, they will be prompted with a very specific choice of whether or not they will allow an app to track their data. If users choose 'Allow', then it's business as usual. If, however, they choose the option 'Ask App Not to Track', the developer cannot track their data and sell it to advertisers.
Apple originally announced the feature in June, 2020 but has delayed till now to give developers time to adapt to the changes. Finally, it's live and app developers must comply.
Why Facebook is against this
Apple's new features were welcomed by many, including policymakers and consumer rights groups. But obviously, it didn't make a lot of people happy. So far, the strongest objection to this new feature came from Facebook. Facebook argued, often by taking out full page newspaper ads, that Apple's new system will make it difficult and expensive for ad networks to target customers, hurting small businesses and content websites that rely on these ad campaigns.
Apple, however, is allowing companies a chance to make their case to users. App developers will have freedom over specifically when to show the choice prompt, to give apps like Facebook a chance to make their case to users about why they should allow data tracking.