But again, like the author said, they're pretty useful for truly global events from the OS itself. For instance, when the keyboard notification fires, it comes

But again, like the author said, they're pretty useful for truly global events from the OS itself. For instance, when the keyboard notification fires, it comes with useful information the app can use at runtime like xy coordinates involving the keyboard which can be used to make calculations on your views independent of the device size. Edit: Sorry, just noticed your use of the qualifier "custom" there.