Checking in at over 2 hours, Apple’s WWDC keynote this past Monday was exceedingly long. Naturally, Apple had a lot of ground to cover, with no shortage of new features to introduce. While we’ve already covered some of the cooler new iOS 9 features, there’s one new feature in iOS 9 that will work its magic behind the scenes. You won’t know its there, per se, but you’ll definitely appreciate what it does.

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These days, with high-res photos and storage-hungry apps, it seems that you can never have enough storage on your iPhone. With iOS 9, Apple will be providing developers with tools to significantly reduce the storage payload many apps currently come with. Apple is accomplishing this with a feature it calls “app thinning.”

While Craig Federighi briefly touched on the feature during the WWDC keynote, it’s high-time to delve a bit deeper and explain just what app thinning is and why it has the potential to greatly improve the overall iOS user experience. After all, an iOS device on the brink of running out of storage tends to exhibits sluggish performance.

Here’s the problem with current apps available from the App Store: they’re needlessly big. Ars Technica explains the root of the problem as follows:

Each iOS app binary you download contains a whole bunch of code for a whole bunch of devices—assuming it’s an up-to-date, universal iOS app that supports the iPhone 6 Plus and runs on 32-bit and 64-bit devices, the app contains assets for literally every supported iOS device whether your device needs all that code or not.

As a result, if you’re using an iPhone that isn’t able to take advantage of some of iOS’s newer technologies, you’re downloading a whole lot of useless code to your device. With app thinning, Apple makes it a whole lot easier for developers to split up their apps such that users only download the code that they actually need.

“Devs will still upload complete versions of their apps to the App Store just as they do now,” Ars writes, “and the App Store does the work of compiling and delivering device-specific versions of those apps.”

Apple itself touts the feature as follows:

The App Store and operating system optimize the installation of iOS and watchOS apps by tailoring app delivery to the capabilities of the user’s particular device, with minimal footprint. This optimization, called app thinning, lets you create apps that use the most device features, occupy minimum disk space, and accommodate future updates that can be applied by Apple. Faster downloads and more space for other apps and content provides a better user experience.

It’s hard to argue with that.

Apps that take advantage of app thinning will see their download size reduced by as much as 40%. And given that Apple seemingly seems intent on sticking with its entry level 16GB iPhone, any way to eek out more storage space is very much welcome.

A life long Mac user and Apple enthusiast, Yoni Heisler has been writing about Apple and the tech industry at large for over 6 years. His writing has appeared in Edible Apple, Network World, MacLife, Macworld UK, and most recently, TUAW. When not writing about and analyzing the latest happenings with Apple, Yoni enjoys catching Improv shows in Chicago, playing soccer, and cultivating new TV show addictions, the most recent examples being The Walking Dead and Broad City.