It is (or at least it could be) also testing for and marking bad sectors. If you write blindly to these and then try to read back corrupted data, your system could crash.
I belong to a financial services firm. At end of lease, or when reassigning computers, we gotta give them a DoD-standard wipe, 7 passes with random bytes. (It’s possible to recover data, with the right instruments, from a formatted disk)
I work for one of those as well. We now require full-disk encryption on all desktop PCs and laptops. One side benefit is there’s no need to wipe drives.
Failing that, it’s often cheaper in terms of time to physically destroy disks and buy new ones if you need to be sure data is obliterated.