If im not mistaking, this will give more editting power to the direction of light reflection from a vertice.
If im correct above, then the vertice controlling the color reflection is controlled by this, via vector(3d oriented from vertice position).
And furthermore, if im correct, the vector afftects all the surface corners attached to the vertice position.
I dont think this can split flatmode and smooth, i think that is something else.
Lots of thinking, i will definetly be playing with this option.