"Cast Volumetric Shadow=on/off" vs. "Volumetric Scattering Intensity=0" ? What saves more resources?

Hello, all my PointLights are shining through my Box Brushes(Walls) and this looks bad. I found out two options in the Details: Clicking “Cast Volumetric Shadow=on/off” vs. setting “Volumetric Scattering Intensity from 1 to 0” What saves more resouces?

My problem is >>> When I hover over the “Cast Volumetric Shadow” then it says “Disabling this can save GPU time” :

But if I click it then the fog is turned off and this is what I want. Same like result like turning “Volumetric Scattering Intensity” from 1 to 0.

What do I have to do to turn the fog(including shining through Brush Boxes) OFF ?

Do I have to click the small box (screen shot) and make the blue checkmark OR do I have to turn the 1 to 0 (also seen in the screen shot) ???

Both has the same visual result for me and I want to save resources naturally :laughing:

Hope I could describe it well. Still beginner in English and UE :sweat_smile: