In some cases, caustics are produced by reflecting off surfaces or through objects, but they create a noisy pattern, even with high photon counts, and even when the rest of the scene is perfectly smooth with final gather. In these cases sometimes the light they produce is more important than what they look like. In these cases it might be best to include an option to combine caustic photons with diffuse photons for use with Final Gather in order to produce a smoother image overall.