I went fishing in the Dev guides from Google and came across this. It looks like this permission is used to restore any previous data the app may have had on your device. Say you had downloaded Angry Birds, beat the game, and uninstalled it. If AB left any data on your SD card, that would be considered a "Backup." If you were to ever download the game again, the Restore permission would scan your device looking for that particular backup and automatically restore your data.
In theory, this makes sense, but why is Glu the only one to declare this permission? My personal opinion is they declare as many as possible, not adhering to the programming guidelines. I don't know a ton about Android programming, but I read that just because you declare a permission doesn't mean it has to be used. However, in order for a permission to be used, it must be declared.
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