If I want to saute some onions, I can set it to 300F and focus on the onions. With a stove that controls power instead of temperature, I need to pay attention to how done the onions are as well as how hot the pan seems to be so I can adjust it. With a slowly-responding stove like an electric radiant stove, this is unpleasant.

This is an especially big deal when using a nonstick pan. A temperature-controlled stove is pretty good at automatically avoiding overheating it.