If you use no_auto_bright=1, than any brightening will be disabled, resulting in dark image if your shot is not exposed normally.
With auto_bright, LibRaw will put 1% of pixels (with default options) to saturation.
Today cameras gray point is usually at 12-10-even 7-8% of maximum (so, up to 4 stops from saturation). Raw converters (DPP, ACR, etc) usually use custom tone curves to compress highlights and get gray point back to 18% (so 0.7-1.5EV gray point move is usual)
If you use no_auto_bright=1, than any brightening will be disabled, resulting in dark image if your shot is not exposed normally.
With auto_bright, LibRaw will put 1% of pixels (with default options) to saturation.
Today cameras gray point is usually at 12-10-even 7-8% of maximum (so, up to 4 stops from saturation). Raw converters (DPP, ACR, etc) usually use custom tone curves to compress highlights and get gray point back to 18% (so 0.7-1.5EV gray point move is usual)