Imagine a really dumb guy who couldn't, for some reason, stop his chainsaw. And he attempts to stop it by holding the blade between his tighs, thus causing massive damage to his genitals. So he decides to sue the company for not having a warning on the label against such a situation. The company settles out of court and of course thinks it's better to be safe than sorry. And thus, we'd have such a warning on chainsaws.