Scorching
Imagine preparing a thick sauce.
The surface may look perfectly fine while the food touching the bottom of the pan becomes increasingly hot. Eventually, it can stick and burn.
Stirring helps, but lowering the burner too much may stop the dish from cooking properly.
A diffuser offers another option: keep the heat source on while reducing the intensity of the heat transferred directly to the pan.
That extra control can be valuable when cooking something that needs patience.
Simple Design, Practical Purpose
Part of what makes these tools interesting