Comment 4 for bug 1157710

I've added a simple cleanup option; not sure yet how to get something that works for everyone in an automagic way as the files that are downloaded are not sequential in any way and different versions/revisions can refer to the same file;

Easy options seem to be to clean by age (but how old?)
By age and size if a certain size is passed (which size? How aggressively should we bump the age as the size is not met?)

The other option, which requires downloading all channels for all devices and seeing which files are unreferenced and clean those (useful for aggresive users of devel-proposed).

I would argue that an application developer would use a released version (channel stable) so I don't see why the sdk would need it per se in the future as the can just clean up everything (the few released images)