I was under the impression it depended on the HDD. IF a machine is powered off, and the HDD has a "parking" sector or two, then it's less likely that the arm holding the head will scrrrrrraape across the platter into areas that hold data.
I can vouch that if a laptop is powered on, that risk is much higher, even with a "parking sector". But it's been a long time since I really looked at HDD specs.
This is also why lately we use SSD's at work, less likely to scrape/damage and the faster speed is one heck of a benefit too.