My moodledata folder currently has 11G of backup*.zip files in the various courses' backupdata folders. I believe most of these are created by using import and I think that it would be good manners if import cleaned up after itself. In cases where teachers are backing up their sites, I think that it would be helpful to allow the administrator to control how many copies of the same course are maintained in the backupdata folder. In the Administration block there is a set of options for scheduled backups. One of them reads "How many recent backups for each course do you want to keep? (older ones will be deleted automatically)". I think that variable would be an ideal candidate for import and backup to use. If the number of backup*.zip files in the backupdata folder is greater than the value set for the number of recent backups to keep then delete the older ones until we have the number that we wish to keep. Whatever logic is used for the site scheduled backups IMHO should be brought over and applied to the individual course backups (including the zip files created by doing imports).