LPM switcher – a special type of material. When you render through LPM (depending on the current rendering engine) it applies material from renderer respective slot to the object. If you render the normal way, then the “Fallback” material applies. This material is useful when you render the same object by different engines in different passes.
Note: LPM switcher does not automatically convert one material into another, it only substitutes the material from the slots in accordance with the current engine.