Google Play Store makes every effort to help you save data while updating applications.
The application updates are usually 20 to 30% of full size.
If the application does not contain .obb (expansion) of files, file patching techniques will be used to update the .apk on the data partition. For the first update of an application system, the application update is downloaded in its entirety once / data / app, such as the partition / system is read-only devices without root and patch file can not be done there . Also, once this first update is complete, the file patch techniques are applied to reduce the amount of data required for the download.
This does not apply as a set of files .obb applications, as these are stored in the external storage and have a different, independent mechanism patching.
Updating an application through the Play Store save the data already, in fact, Google considers it a violation of the Terms of Service if developers to distribute applications through the Play Store is used to update other means that Google Play the mechanism itself.