Even using a DOD 5220.22M compliant erasure program can leave little wisps of magnetic inferences around the outside edge of the tracks.

This becomes more and more true as we go higher and higher in disk density. The higher the density, the higher the reluctance of the magnetic media (typically) and the more "sticky" the bits.

A buddy and I in Eureka tried for a couple of years to come up with a [relatively] compact electromagnet that could de-gauss a drive in less than 30 seconds. As drive densities have increased (radically) in the last few years, it has become harder and harder to degauss a drive - and we're talking some big, big electromagnets we were using here.

Hence, this is why I like physical destruction.