Re: OOC: Literally, Everything Else Ever
And you ALWAYS power down a computer before you unplug it. Always. Many, many applications, especially linux-based stuff, will not write everything to the harddrive. They will keep it cached in memory, and only periodically write things to the harddrive as needed or when idle, and even then it may be incomplete.
If you unplug a computer while it's running, especially if it's in the middle of happily running windows or another OS, you could seriously fuck up your shit. The odds of this happening are about 1/5000 for modern windows and a little higher for linux/macOS (heavily depending on your distribution), but you roll that 1/5000 chance enough times and it becomes pretty likely.
Anything with moving parts being unplugged while in operation, like your harddrive spinning around at 120-250 rotations per second, should definitely be powered down or in an idle state before having the power cut abruptly.
TL;DR:
Computers are not appliances. Shut them off before yanking the cable.