Any stirring, kneading, mixing, or working of a batter or dough causes gluten, a natural protein in wheat flour, to develop strands. This makes cakes tough, muffins leathery, and scones basically unfriendly. When a recipe says, “stir or knead only as much as necessary to combine the ingredients,” it's telling you that you should avoid developing the gluten in this recipe, lest your product becomes tough as nails. Who eats nails?