If this function is paired with VertexLitGeneric material, this function will reuse light parameters calculated on previously drawn model unless other are specified using render library (such as render.ResetModelLighting). If you experience lighting issues or you want engine to calculate light for you, draw a dummy (invisible) model in origin of mesh, then draw the mesh.

If utilized inside ENTITY:Draw, drawing entity's model (if it has one) should be enough.