Tightening wheel nuts: Why is it so important?

Let's be honest: How often do you check the tightness of your wheel nuts (and wheel bolts)? Once the wheels have been fitted and the wheel bolts tightened, everything is ready – isn't it? Not quite! When it comes to safety, it is very important to check the seating of the wheels from time to time, and not just after a tyre change. But why do you have to tighten the wheel nuts?

Barum. A brand of Continental.
Good tyres. Good deal.