Why Is PostQuitMessage Necessary

Question

Pretty simple question. I was just curious why I would use PostQuitMessage(0) to break out of my Message Loop, instead of just doing something like:

bool isRunning;

case WM_DESTROY:
{
    isRunning = false;
    break;
}

Honestly, I don't really see any harm in doing it this way, but maybe there is some minutia I am not quite seeing.