Back at Google I/O in late June, it was announced that Smart App Updates were coming to the Play Store and that time has come. The latest version of the Play Store (3.8.15) which will gradually roll out to users includes this functionality.
Smart App Updates can be best explained by the Android Developers website:
“Smart app updates is a new feature of Google Play that introduces a better way of delivering app updates to devices. When developers publish an update, Google Play now delivers only the bits that have changed to devices, rather than the entire APK. This makes the updates much lighter-weight in most cases, so they are faster to download, save the device’s battery, and conserve bandwidth usage on users’ mobile data plan. On average, a smart app update is about 1/3 the size of a full APK update.”
It won't be the most noticeable update at the end of the day, but it will help cut down on the bandwidth required for updates and happens without any input from the end user.
KitGuru says: Next time that application update on your Android device is rather small, don't worry, it's just Smart App Updates doing its job.