Just to clarify something.
many people misunderstand the term 'maximizing dynamic range".
They often think that means getting the most SPL out of the system.
that is totally incorrect. The max SPL is purely limited by the loudspeakers and the amps driving them.
You cannot get anymore out of it. Now granted with some creative limiting you can increase the apparent SPL-but that is operating the system in a non linear fashion.
What "getting the most dynamic range" really means is making the system QUIETER-NOT louder.
By setting the gain structure properly you can effectively lower the noise floor.
how important is that? In some cases it is VERY VERY important-and in other (most) cases it really doesn't matter. Gear these days is much quieter than it was "back in the day"-ESPECIALLY early digital devices.
Having a visual reference on the console has nothing to do with getting the gain structure correct-but everything to do with setting a reference for the console.
This could be 1 of several different setups. Maybe the peak light on the console matches the peak light on the powered speakers. Maybe 0dB on the console matches the peak lights on the loudspeakers.
Or maybe 0dB on the console means some particular SPL at some position.
Without knowing what the exact requirements of "setting the gain structure" actually means-there are any number of different answers to the question.