Apple's iOS 9 brings a lot of good stuff to the table, but there's one feature in particular that seems long overdue (and likewise, should be available on alternative platforms): "App Slicing". What this allows developers to do is mark assets within their app as being for specific device platforms so that space is not wasted.
Traditionally, users who download an app get the entire thing regardless of whether or not they'll make use of some of its contents; App Slicing could send one build to the iPhone and completely different one to the iPad. This feature is mainly geared at iOS users that are burdened with 8GB and 16GB storage capacities (Apple is still pushing 16GB with the new iPhone 6S and iPhone 6S Plus). Overall, it's a neat feature, and the only way it seems like it could be made better is if users were able to enable a setting that would always downloaded the smallest version of the app.
App Slicing design; Credit: Ars Technica
Nonetheless, despite how cool this feature is, it's not yet ready for primetime due to a backup bug that exists within iCloud. Apple relayed this message to developers through its official developer portal:
App slicing is currently unavailable for iOS 9 apps due to an issue affecting iCloud backups created from iOS 9 where some apps from the App Store would only restore to the same model of iOS device.
When a customer downloads your iOS 9 app, they will get the Universal version of your app, rather than the variant specific for their device type. TestFlight will continue to deliver variants for your internal testers. App slicing will be reenabled with a future software update. No action is needed by you at this time.
Fortunately, developers don't need to do anything different right now; they can still continue to develop with App Slicing in mind. It's just that regular users will continue to get the full-blown apps anyway, until this bug is obliterated. Now, how about you follow Apple's lead, Google?