App extensions in iOS are probably not used, understood, or even known about as much as they should be. They're probably exciting the tech geek crowd more than anyone else, especially the Android-to-iOS audience that missed the powerful things they could do before trading their Nexus in for an iPhone. But app extensions have fundamentally changed the way apps work and the way they can deliver value to iPhone users. Here's why.
Prior to iOS 8, 3rd party applications were almost entirely self contained experiences. With the exception of a few tricks that paired partnered apps together (and most often apps in the same developer ecosystem, e.g., Google), the only way you used an application was opening it directly, using it for its purpose, and closing it. With iOS 8 apps have a newfound ability to contribute to the iOS operating system. Apps can now provide features and functionalities for the rest of your apps to use indiscriminately. And many of these functions mean you never have to open certain apps again, while benefiting massively from what they have to offer.
Take the new ability to include lock screen widgets with 3rd party applications. These widgets can be so robust that many times the full function of the application can be moved out of the app. For example, I installed Yahoo! Weather because the lock screen widget provides and instantly glanceable, beautiful, informative view of the weather. Now that I have the Yahoo! Weather lock screen widget I will probably never open the actual application again.
It doesn't stop there. Apps can add camera functions and keyboards too. I rarely used Camera+ because I often take pictures with Instagram or VSCO Cam like most people, but now I can easily edit photos in my iPhone camera role with Camera+'s functions when I want to. And finally I can use Swype's unique one finger keyboard, the former Android exclusive pride and joy, to write emails. After installing the Swype app to get the keyboard there is definitively into reason to open the app again.
With all of these new capabilities, what it means to be an iPhone application is being completely rethought and reimagined. I'm excited to see the things developers create with this powerful new opportunity in iOS.