Formating a drive does not destroy the data. It disassoicates the data from file structure. It is like having a library full of books and destorying the card catology. The books are still there, you just have no organized way to find them. Certian programs can rebuild "The card catology" so that the data can be recoverd. With the drive being formatted the OS will not warn you, you are about to overwrite the data. You can still, in theroy recover the data till that porition of the drive is overwritten.
Wiping a drive overwrites every place on the drive. This destroys the data making it very hard to recover. A Quick
wipe overwrites the data with one pass. The DoD
wipe overwrite, or passes over, 7 times. The Gutman Wipe overwrites the data 35 times. This is Black Helicopter paranoid.
Wiping a drive is like using a piece of carbon paper. The first pass you can read it perfectly. With each addional pass the carbon is harder to read.
Formatting a drive with virus' will not destroy them. If the new OS overwrite them while setting up or writing data to the drive, that will damage or destroy them.
I wipe every drive prior to installing an OS or data. I have know many more that simply format thier drive and reinstalled, never having a problem.
One note. A large hard drive, 40gb+, can take 24 hour + to wipe compared to a format that may that 30 minutes to and hour.