Please correct me if I'm wrong, but I thought that the 'softness' of shadows is more to do with the actual light rather than the shadows? The more diffused the light source, then the softer the shadow; the more intense and direct the light source then the crisper the shadow. An emissive material will give the max softness, a spotlight the max crispness and IES profiles give all the ranges in between.
(Although I am 110% behind giving native Enscape light sources a "diffuse" setting.)
Yes yes Gadget , that's 100% true, usually the size of the light source, the distance from the subject and the intensity affects the softness/sharpness of the shadow. I was just saying that you loose a lot of details when the shadow is really soft.