[chuckadams]

On the Commodore 64, you knew your floppy was bad when the drive would reset itself, slamming the read/write head against the stop repeatedly. “tick-tick-tick-tick-BRRRAAAAAAP” ... eventually knocking the head out of alignment, requiring a hardware fix (not a difficult fix, but tedious). Copy protection was notorious for causing drive knocking, so people often used cracked versions of games they purchased just to prevent it (they tended to load much faster too).

[nubinetwork]

The 1541 doesn't have a track 0 sensor, so they send it 40 step commands to move it back to 0. If it wasn't already on track 40, it will just bump against the stop repeatedly. I've never heard of it damaging the drive though.

[chuckadams]

My own 1541 never actually had problems, but it was folklore on BBS's, and I saw it happen with my brother's drive. Was easy enough to service though, just loosen a couple screws, nudge the motor a teensy bit, run a diagnostic disk, and repeat ... many many times. They might have just been prone to misalignment anyway, but the knocking couldn't possibly have helped.

[calamari4065]

It's a commonly cited source of head misalignment. I'm not sure if that claim is true or not though.