Originally posted here by !mitationRust
DoD 5220-22.M is not good enough for top-secret data destruction. Those platters are electronically, chemically and physically "destroyed”.
While this is true, it's also true that three overwrite passes is sufficient to deal with Secret-level data destruction, according to DoD specs, and that's not small potatoes, either.

The bottom line is that if your data is absolutely priceless, and interested people with endless resources will go to any lengths to recover it, then yeah, physically destroy the drive. Otherwise, overwriting it with a few passes of random data is probably more than enough.