@ PotatoZero
For stir frying something like broccoli or cooking dumplings or thick sausages, it's useful to add some water and cover it in order to allow it to steam a bit. This allows the entire thing to cook and heat to reach the center without burning it. In the case of dumplings and sausages, you can make them crispy again after removing the lid.
As for frying, you don't need half the height to fry things, since you can stir them around to get full coverage. By the time you add half the height in oil, you're practically deep frying, I'd say.