Also, you can use the “raytracing quality switch” node in materials to make a material shiny in normal view, but matte in reflections to eliminate noise. You can use cube mapping to fake reflectance in the raytraced material. Usually, it is not important for reflections of reflections to be physically accurate.
It wasn’t that long ago that lumen couldn’t reflect reflective surfaces at all, and they would either be forced to appear matte, or would show as pitch black.
During that time, I demonstrated a method for creating a cube mapped fallback reflection.
This method has 0 noise issues. While it has the typical flaws of any cube-mapping technique, this was one of the standard approaches to car reflections in driving games before raytracing anyway and makes for a good fallback on secondary bounces.
Here is a writeup about it:
And here’s a YouTube video:
Again, keep in mind this content pre-dates lumens multi bounce functionality so some things may be slightly outdated.