The Illusion of Deleting Digital Data
Simply dragging a file to the trash does not actually erase it. Software-based data sanitization works by permanently overwriting every sector of a drive, turning old information into unrecoverable gibberish.
When you delete a file normally, your computer merely marks the space as available for new data, leaving the original content hidden but intact. Professional data erasure tools go much further by writing patterns of random characters over the entire drive. This irreversible process ensures that even advanced forensic recovery methods cannot reconstruct the original files. It is the only way to truly sanitize a device before handing it over to someone else.
Source: Data erasure