There is no performance advantage once you have flipped a switch; it effectively becomes a new material then. The main gains there are in keeping consistency and making workflow easier. If it becomes more work to wire a bunch of complicated stuff into one material, it might be counter productive. There is also the shader compile time to consider. If everything in your game used one huge swiss army material, any change to that material will kick of a TON of shader compiles. Keeping things reasonably broken up by different types makes sense to keep thing from happening. It’s all about balancing consistency and complexity. There is really no rule as to when one or the other becomes more important.