For example, the following figure shows two lights, one with Draw Volumetric Light activated and one with Draw Volumetric Light disabled. If you set Fog Intensity to 0, the Draw Volumetric Light settings have no effect.

Draw Volumetric Light A. Activated B. Disabled
 Except where otherwise noted, this work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License
 Except where otherwise noted, this work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License