Today, Google launched a couple new features for developers that will give them a lot more flexibility in storing data associated with apps. For starters, using what's called "app data folders," a developer can store important files in a user's Drive storage space. This is huge news as, up until this point, the main method for backing up data has been the Backup API, which is great for small things that are 1-2MB or so, but isn't really sufficient for larger files.
Lest you worry that developers can now pile a bunch of data into your Drive account, users will still be able to see how much data is being stored. Just not what's in there. Developers can instruct their app to retrieve this data at any time so, while it's not a proper sync service, it could potentially be used to retrieve game saves or configuration files when installing on a new device.
Additionally, Google is allowing devs to add custom properties to any Drive file. This would allow apps to apply arbitrary metadata and utilize that for its own functions. One example given is that "a classroom app could keep track of the grade for a document."
These two features are small, but powerful options that hopefully developers will find plenty of use for. If any devs in the audience have some ideas for how they might use them, feel free to share in the comments.