This script is handy when you want to sell or give away an old flash or disk drive, and you want some certainty that files on the drive are not easily recoverable. First erase all the files on the drive, then run this script. After it finishes, all user-writable areas of the disk will have been written over with zeroes. You should be transferring ownership of the drive to someone who is unlikely to attempt to recover files from the drive, and you should not have highly sensitive information on the disk.
If you need something more secure check out these articles, below.