"On the other hand, users (as distinct from developers) are about to see an upside of Apple's monopoly power. The next update of its mobile operating system, iOS14, includes a change that should have a dire impact on many online advertisers. The industry assigns a unique code to each device called an IDFA. Knowing your IDFA can help advertisers tell whether their ads are effective, particularly when they've shown you the same ad in multiple places. Facebook uses the IDFA as part of Audience Network, its ad network for developers."