Why does mocha need to be in devDependencies?

On the face of it, mocha being in devDependencies like the tutorials say, is logical enough, it is after all a dev dependency.

But in practice you install it -g so you can run mocha as a command. And as far as I can tell, given that, it makes no difference at all whether it's mentioned in your package.json.

So is there any need to explicitly list it?

via rwallace