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When would you use irradience caching vs non irradience cached light mapping? I usually get longer render times, and a more splotchy render.

Irradiancecaching speeds up rendering very much in low to mid range light situations. If you use very strong lights and therefore produce high contrast in your image, irradiancecaching can produce alot of splotches. To get rid of the splotches you have to raise finalgathering.
If you turn off irradiance caching it's more of a bruteforce calculation but can produce better and faster images with less amounts of FG if you have very strong direct/indirect lights. They outcome will look more like Fprime or Maxwell.

By turning off irradiance caching, you will essentially get the same amount of splotches, only it will be per-pixel noise instead of splotches. Not really less of it, as such. However, per-pixel noise is MUCH easier to filter out with something like NeatImage than irradiance caching splotches and artifacts are.