We have a lot of data that we want to back up for our users, but we also don't want to back up all the data. Let's say we all agree not to back up users' passwords or other sensitive data, but what if you have a specific app configuration that is generated based on the device the user is using? This too should be excluded in a manner similar to device tokens such as Google Cloud Messaging (GCM) and others. I would recommend that you figure out which data your app keeps persistently and whether this data should and can be device-agnostic.

You can configure what is being backed up besides the automatically excluded files mentioned earlier. This configuration should be declared in your app's manifest via the android:fullBackupContent attribute. You will need to create a new XML file that should reside in your res/xml folder, and this will have specific rules for the backing up of your app's data.