For example, I was hiking (or tramping as it's called in NZ) with a foreign friend visiting. They were unlucky and broke an ankle. We called the police, a helicopter was dispatched, picked her up, brought her to the hospital and fixed the ankle up. Zero cost to her.
One of the many upsides is that it's quite difficult to sue for personal injuries in NZ - as ACC basically covers the costs (or at least, that's my understanding anyway)
Sure there are downsides to any system, and some people do fall through the cracks of ACC, but on balance, I think it's one of the best things about NZ (besides the nice relaxed atmosphere and killer scenery)