Customers have long asked Apple to ditch the 16 GB iPhone and offer a 32 GB entry-level device instead. However, Apple has kept the 16 GB variant of the iPhone 6s and iPhone 6s Plus, promising to offer new iOS 9 features that will considerably reduce the size of apps and free up space.

One of these is app slicing, which is targeted more towards developers than consumers. App slicing is a neat feature that allows the iPhone to recognize only certain app assets needed to run properly on the phone.

For instance, an iPhone 5 will only download app assets designed for the iPhone 5. It does not need larger images that are designed for the 5.5-inch iPhone 6 Plus or 64-bit code that the iPhone 5's 32-bit chipset will not recognize. It will also do away with graphics built on Metal, as the older iPhone's graphics card will not be able to run the new graphics.

So even though most users will not see app slicing as a user-facing feature, they will largely benefit from it, especially users who have a 16 GB iPhone, as it gets rid of unneeded assets and opens up space in the iPhone.

Unfortunately, app slicing will not be available for iOS 9 for now. Apple has announced on its developer website that it is pulling out the feature due to problems with iCloud that is preventing some app backups to restore to newer devices. For instance, users who are upgrading from the iPhone 5 to the iPhone 6s will have the iPhone 5 version of some apps when they restore their app backups from iCloud, leaving out the iPhone 6s-specific assets that the apps need to run properly on the newer device.

"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," Apple says.

Until Apple finds a fix for the iCloud bug, iPhones running on iOS 9 will have to download the universal version of apps, which will download all app assets, which is sure to eat up a lot of space quickly. However, users who are on TestFlight, Apple's beta app distribution program, will still receive device-specific assets.

App slicing is one of three app thinning features-the other two being On Demand Resources and Bitcode-- that Apple introduced in iOS 9 to reduce the space taken up by apps as a way to encourage customers to buy 16 GB iPhones.