Interactions with iCloud
While Apple does not appear to track what you actually do in iCloud, it certainly knows when you are using the service. That includes every time you download data from iCloud (access a photo, download contacts, etc.), and every time you (or an app) uses the email account your iCloud service is connected to. This is all about studying the frequency of use for the service, one of the most common types of mobile data for any app to collect, and something that is unlikely to change in the foreseeable future.