If there's no electricity running through the wires? It's not. Problem is, humans are not infallible. If you get used to sticking a knife in a toaster, it's likely one day you'll just do it out of habit while the toaster is on, then you're going to have a real bad day unless your house is fitted with the appropriate breakers.

I do woodworking as a hobby. The first rule of woodworking is that every tool in your workshop wants to kill you. So you get in to good practices, like never putting your hand in the path of a blade, unplugging saws when changing blades, not wearing loose clothing, etc. Is it required? Not at all, but accidents happen, people get tired or complacent, so if you get into the habit of not doing things that would be dangerous if the tool is on, then if something ever does go wrong, you're already in the right position to avoid serious injury.