Shadow smoothing is in the light tab of the atmosphere editor. It has nothing to do with soft shadows of direct lights (sun, spots...), but it reduces noise produced by indirect shadows (in advanced lighting modes, such as AO, GI and GR) It is highly important when using GR, which by default always produces noise, but not so much for other lighting models that are pretty clean in Vue with default settings ( a good point for Vue, in C4D, you need to push the quality pretty high to get smooth AO shadows)