When you launch applications, from the built-in memory or the Expansion Card, they save data onto your device.
This data is used by the application when active, and normally, will be deleted when you delete the application itself. Some applications, intentionally or by a programming error, save items under a different Creator ID than their own; these items will remain on your device, occupying your handheld's memory. This program helps you get rid of this data to free up memory on your device. | 
