Erases all files and hidden data on a storage media really and completely, so to prevent your information properties leaking out.
When you remove files on your disk with Explorer and other ordinary ways, the files may not be erased really. Even formatting disks may not erase data really. They - files and data - may be just marked as hidden, so that you recognize they are removed. Some data recovery software can revive them from the disk, or may pick up some fragments of the data. When disposing or passing a storage media to someone to transport information, through these hidden data blocks on the media, your important information properties may leak out of your control.
Disk Secure Eraser erases disk contents with a method which prevents such data capturing actions.