When adding iCloud support to iOS app one can configure iCloud Display Set and link it with an app by specifying NSUbiquitousDisplaySet. But iCloud works even without it, so my question is: what's the purpose of iCloud Display Sets at all?
Couldn't find any clear answer anywhere in the docs. And what's more, based on the Apple docs it seems as if specifying Display Set for your app was mandatory if you use iCloud. That did confuse me a bit.
It is so that one might want to share the same Display Set for multiple applications or for iOS and Mac app versions?
That's right, it's for allowing multiple apps to access the same mobile data store.
From the Information Property List Key Reference:
NSUbiquitousDisplaySet (String - iOS, Mac OS X) contains the identifier string that you configured in iTunesConnect for managing your application’s storage. The assigned display set determines from which mobile data folder (in the user’s mobile account) the application retrieves its data files.
If you create multiple applications, you can use the same display set for your applications or assign different display sets to each. For example, if you create a lite version of your application, in addition to a full-featured version, you might use the same display set for both versions because they create and use the same basic data files. Each application should recognize the file types stored in its mobile data folder and be able to open them.
来源：https://stackoverflow.com/questions/9476060/whats-the-use-of-icloud-display-sets