Snapshot Pro, Dropbox, and archive retention

Snapshot Pro has fantastic potential, but I can't for the life of me figure out how to set file retention. For example, if I set it to back up to Dropbox, at what point will it start deleting files from Dropbox? Or will it just keep writing new files until my drive is over capacity? If this is the case, what an oversight. Every other notable wordpress backup program has the capability to set a remote file retention duration.

Am I missing something?