Not a master on the subject but I believe it'd be a good practice if we adjust ourselves with both the grips as sometimes we are working on larger drawings that we can't really cover with our wrists. Over the hand allows you to put your whole hand in motion and gives better flow to your lines. But yes when you're working with details and comparatively smaller work I believe it's okay to use your wrists. Its just that you should not feel limited because you are not accustomed to the other thing.