Whats the point of .6 .8 nozzles

[Hobo4ssassin]

I also just saw this post, same concept

Max Volumetric Speed - Limit - How to find the maximum/optimum value

So I understand that this setting prevents clogs by not allowing overspeed of filament flow of certain filaments. I see PLA has a higher value than generic PETG. Has anyone tried to set an optimal value for a given filament? Is there a test or something? Any info welcomed!