I don’t know the inner workings of LightingMode MultiPass rendering.
Since there are no hints or flags or so, I’m assuming (tho certain values maybe aren’t actually updated), the entire shaders are run each pass. Even values that are invariant (like the verts distance from the camera) has to be re-calculated.
Am I way off here? 
Yes all these values are recalculated each time. There’s no way to avoid it besides either doing it singlepass or deferred rendering.
If you manage the lights properly, like bake static lighting and only attach lights in places that need them, you can avoid these computations
Ok. I’m going with singlepass i think because its just grass quads with vertex lighting it can all be done in one pass, all of it in the vert shader.
Thanks.