I've used such tools to wipe my hard drives before selling or donating used computers (although I would use them before disposing of a hard drive in any way, really). I have heard of people buying up used computers and hard drives and extracting saved passwords from them.
A lot of people are smart enough to format it quickly, but not everyone will let (or know to) a computer sit for dozens of hours so that things might be wiped more securely.
I've had the experience where people agree to buy my broken computers for parts and the deal is done, until I mention that the "drives are wiped and ready to go". Then I never hear from them again.
Granted, somehow visiting the craigslist site turns ordinary people into flakes, but the "wiped" statement correlates a bit too well with the vanishing interest.
+1, but I'd stop mentioning it after the first time (unless of course you're just doing this as an experiment and aren't really interested in selling the stuff)
A lot of people are smart enough to format it quickly, but not everyone will let (or know to) a computer sit for dozens of hours so that things might be wiped more securely.