Rating episodes is a way of marking your favorites and when you like to reach your favorite episodes thru Ziepod, 'Rated Episodes' build-in bin helps you with that. If it is enabled, Ziepod automatically keeps a pointer to rated episode inside.
'Rated Episodes' bin comes in enabled mode. When you disable it, all rated episodes are kept as they are but pointers to those are deleted only. When you re-enable it via Preferences Dialog, Ziepod traverses all subscribed feeds and gathers pointers those those rated episodes. Keep in mind that that process may take time.
'Rated Episodes' bin is represented with ( ) icon in the folder hierarchy.