Light emitter is a completely WRONG name and this creates confusion.

All this checkbox means is that , as in real life, every object that recieves light does diffuse that light into its surroundings. => Creating In Direct Light.

Turn the checkbox OFF, and the object does not diffuse incoming light back into its surroundings.

A better name would have been Light diffuser, or Indirect Light Diffusor.

As all Real life Objects do....full time.

Ony a black hole in space is a NO Light diffuser.

Your conclusion and findings are corrrect.
With IDL ON, you need far less Direct light then without IDL.

Total light in the scene, is the Direct Light + the InDirect Light provided by all objects diffusing the Direct Light.

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