In the Star Wars movies stormtroopers tend to die from a single hit no matter from what weapon or on what location. A single blaster hit anywhere on their armor is all that is needed to take them out. Even hitting them with a wooden stick or small stones seems to be lethal to them.

If that is the case, what is their armor good for? Has there been any example of a stormtrooper's armor protecting him from any harm?

Durasteel armor would be very effective against gunpowder weapons, this is why slug-throwers are hardly ever used, but as they don't face such weapons on a regular basis, what threats are on a battlefield against which the stormtrooper's armor provides protection?