@Ghostship. I've checked that. There's no difference in bounced light between the two options.
The ball in the centre is the emitter. The ball on the left has "light emitter" enabled, the ball on the right has it disabled.

The "light emitter" option already exists in many older versions when there was only the FireFly render-engine. Indirect light in Firefly
gives quite poor results and takes ages to render when you increase the quality to acceptable results. I assume they added this option
so users can include and exclude specific ambient materials to emit or not emit light light and prevent unnecessary processing time.
At least that's the the way I've used it on some models. There should have been a reason for the developers to include the option I'd say.