The downside to buying the 16GB iPhone or iPad is that you find yourself running out of storage space very quickly, but the good news is that with iOS 9, Apple will finally address that issue with a feature called "App Thinning". This was briefly mentioned by Apple's Craig Federighi during the WWDC keynote, but the folks at ArsTechnica have broken it down further.
Basically the idea behind app thinning is that it will exclude data that you don't need from the download. As it stands, every app you download contains assets for literally every supported iOS device. This is regardless of whether you will need that data, so for example if you're running an iPhone 4 that can't take advantage of certain features of an app that is only available for iPhone 5 and above, the app will download all those assets anyway.
This means that your phone is storing a bunch of data that you will never ever need. This is the equivalent of software developers who bundle Windows and Mac softwares together in a single file, just in case you might install it on a Windows or Mac computer. It is redundant. So with iOS 9's app thinning, the iTunes App Store will be able to work out the data that you need and delivery it accordingly.
Original Article: http://www.ubergizmo.com/2015/06/ios-9-app-thinning/?utm_source=mainrss