I used a light bar above the windshield for years on my JKU and the only two issues I encountered were 1. whistling wind noise at highway speeds and 2. Discoloration on my A-pillars from the light bar brackets. Would I do it again? No.
I intend to go with a front bumper bracket mounted light...
That knob does control the light on the inside door handles of my 2021 Gladiator Sport S. It's so dim you almost need to be at the bottom of the Mariana Trench to see it.