What is the difference between storing your coin on a trezor, vs some random hard drive that you unplug from your computer? I currently store on a trezor, but after talking to a friend I'm beginning to wonder if it was necessary. IE, as waste of money. My buddy just have a cheap USB Hard drive enclosure, and when he installed all his wallets, he simply told them to install to that hard drive. Which he leaves unplugged from the computer, unless he's actually moving some money around for whatever reason. So it always just stays unplugged, just like my trezor.

What is the difference? Why buy a Trezor when you can do this? Hell why even go that far? Why not just use a USB flash drive that you already have lying around? And just leave it unplugged when you're not moving money around.