Fog delicately emphasizes light sources, as if giving them character. It adds depth where there was none before, as if light gains a new dimension and stops being flat. You can suddenly see the whole path from the source to the illuminated surface.
Photographing in fog is pure pleasure. In a frame, those light characters begin to perform: one shines in a direct beam, another in a diffused glow. Different temperatures of light and different directions of the beams make your eye jump between accents as you look at the photograph.