You’ve just returned home after a good day of work. You’re outside your house with two hungry kids and a horrible weather. When you’re about to unlock your door you don’t find your keys. And suddenly you remember where they are.
Safely placed at the back of a computer at work. Always remembering your USB key because it is placed on your key chain = a good idea. Forgetting your keys at work because they are securely fastened to your USB key = bad idea.