Sometimes, we need to completely and irreversibly wipe all data contained in a disk to keep them from falling into the wrong hands.
This may not be something we are doing on a day to day basis, but if you want to do it, you should do it right and ensure that the data cannot be recovered by experts. One of the many ways of doing this is through Darik’s Boot and Nuke bootable live CD. This tool is made from the same team that develops the professional-grade Blancco data eraser, only it is available for free and without guarantee or support. The reason I like DBaN is because it is very simple to use and does the job fast.