Hello vincismurf,
Thank you for getting in touch!
The "Add Pass" in the rendering options allows the shader to support all scene lights, toggling it off is equivalent to the Unity's Shader Language parameter
"noforwardadd", disabling the forward rendering pass so that the shader only supports one full directional light, which could be useful to optimize the shader for mobile applications.
Do you happen to be looking for Multi-Pass support? It should be available soon via
Shader Templates!
Please let me know if you have any further questions, thanks!