> The only things that comes to mind is to correlate device ids from different apps if the apps use the same analytics/advertising networks. A long time ago, d

> The only things that comes to mind is to correlate device ids from different apps if the apps use the same analytics/advertising networks. A long time ago, device IDs were available to apps. But that changed because those are typically immutable and the user has no control on revealing a different one to apps. So the makers of the operating systems brought a new identifier (IDFA in Apple’s OSes) that can be controlled through settings. Even before the forthcoming iOS update, you could just turn off cross app tracking completely by turning on Settings->Privacy->Advertising->Limit Ad Tracking in previous versions. But this was off by default, meaning tracking was allowed unless disabled by the user. Now it’s an explicit prompt when an app asks for the IDFA. The IDFA can be used to uniquely identify and connect a user across apps.