A very underrated and perhaps overlooked feature.
I was thinking of adding a mouthwash bottle to a scene, but when it came to shadow casting, I remember there is no way to get caustics from a real time light source.
But it’s not just the mouthwash bottle. Wine glasses, jewellery and even plastic filled with water will cast caustic like shadows.
As for why dynamic and not bake it through lightmass, have you ever observed a car during a very sunny day? If the angle is just right, you’ll see metal parts of the car rim projecting caustics on the road!
This is the closest image I could find demonstrating this effect.
I’m not fully aware of what technology is needed to pull it off, but I have found some examples of it being done in real time:
Real-Time Caustics in Dynamic Scenes with Multiple Directional Lights https://youtube.com/watch?v=LlkclF6b0Tc
Real Time Caustics Whitepaper
Caustics Mapping: An Image-space Technique for Real-time Caustics
Real-Time Caustics Using Screen Space Directional Occlusion
Fast Real-time Caustics from Height Fields