With some apps, the size of an initial download or an update can make or break an app's popularity. Even if things aren't quite as dramatic for some apps, it can't hurt to save users some of their data allotment when they're updating your app. On that note, Google has rolled out a new Play Store feature for developers that automatically saves users about 65% of their data, on average, versus the old way of updating, which required a user's device to redownload the entire app. The data savings over the current method is between 10% and 15%, depending on the app.
The new update method being rolled out consists of patching apps that need to be updated on a file by file basis. Individual files, rather than being replaced, are actually ripped open and individually modified with the new code. This stands in stark contrast to the current method, called Deflate. Deflate's compression prowess is considerable, but small changes in an original file can be hard to track. Essentially, in this new method, the Play Store compares the version of the app on a user's device against the new files coming down the pipeline, and opens the files up to make changes. Only the bits that are actually needed for the patch are sent through, meaning that the update cuts into a user's data allotment as little as is possible for the update to happen successfully. It also means that updates happen faster, and with the patcher no longer replacing groups of files wholesale, there's less room for error when updating an app.
The new patching method is already starting to roll out, and developers won't have to lift a finger. Developers and users should start seeing the changes in the coming weeks, and eventually, every app published through the Play Store will be making use of this new update method. For the time being, since compression, file change, and then decompression can be a somewhat long process, Google is limiting the rollout of the new update method to auto-updates that tend to happen while a user isn't actively using their device, such as while they're sleeping.