Earlier quoted context omitted.
Follow up question, as someone who knows even less about forensics, what kind of traces stay on a hard drive if you just delete a file?
A lot. You need to write a drive with zeros(minimum)/random data(preferably) at least once to make forensic recovery difficult. I know all about the "5 times" rule, but I've never heard of anyone recovering a drive after even a single overwrite. Personally, I just hammer a screwdriver through the platter. It generally converts it into glass shards--the drive sounds like a maraca afterward. Flash, of course, is differ…
SSDs won't necessarily actually erase a block when you tell them to, due to wear-leveling and weird internal RAID setups they could be doing anything in there.