Pixar's New Global Illumination

Instead of building reflections and shadows manually, why not do it automatically every time an artist placed a light source? "It was as if every time you took a photograph, you built a new camera," Kalache says. "It takes away from the art of taking a picture. We wanted to stop being engineers and be artists."

Each frame requires 20GB of RAM just to do the ray-tracing, and from what I've seen it's worth all the effort. The Pixar team includes some of the finest artists working anywhere. 

Source: http://www.theverge.com/2013/6/21/4446606/...