Obb is a data file format used by multiple game developers. Data stored in such a format often contains music, videos, and other large files that are downloaded after the APK is installed. This makes the APK smaller and easier for developers to maintain. (Imagine uploading 2 GB file every time when the app gets updated!)

Additional data files are stored in internal storage, which isn't a perfect situation--especially for owners of devices with external SD card support. The internal storage gets full in very short time, even when it's big, so it's a good practice to use the external SD card to keep these obb files. XDA Recognized Developer moneytoo came up with an interesting solution and created an Xposed module to automatically handle obb files. After moving the android/obb folder to the external SD card, those files are “visible” to games. There is no need to play around with it. Just install the module, move your files and don't waste your internal storage.

Since this module runs using Xposed Framework, please make sure that your device is rooted and Xposed is working before giving it a shot. If you are using ART, you will want to revert to Dalvik in order to make this work.

Are you a gamer? If so, head over to the Obb on SD Xposed module thread and give a try.