How safe are my data if my hard drive isn't encrypted?

Permanently Deleted

Except when your drive is encrypted you can easily destroy its contents. Let's say you're DorkPirate1337 who happens to care about their opsec; you luksEncrypt your drive and have a simple script that runs when a specific USB key is disconnected, triggers luksErase, and then poweroffs. Voila, when the school principal snatches your unlocked laptop while you're in the lib, all your pirated hentai becomes permanently unaccessible whether you give up the password or not. [Edit: the USB key is strapped to your wrist]

Note: luks uses 2 encryption keys, where one is randomly generated and encrypts the actual data, and the second one is given by the user and encrypts the first one; luksErase destroys the luks header containing that first key

Not that other means of accessing the passwords aren't worth considering, but in the real world, it takes a lot more for someone to actually coerce your password from you than to use unencrypted storage.

I generally like xkcd, but this is a harmful trivialization of the value of encryption. In the real world, anything that isn't encrypted is negligent as hell. There's no valid reason not to do it, with maybe the exception of a thumb drive you're sharing across a computers you don't control and are clearly aware is not secure.