You need to enable some kind of transparency for SSS to work, same for absorption. I find it unintuitive too but I guess it's still a WIP feature. What I know so far is that for SSS to work, you have to enable some absorption first (change color to other than white and value to other than 0), and then you can change scattering parameters. For me it is easiest to make the material completely transparent first (refraction 1, ior 1, glossiness 1) and then play with SSS parameters. When you are more or less happy with how SSS works, you can change refraction parameters or disable refraction and enable translucency. Refraction + SSS will work like for example fluid that has some kind of tiny particles inside (milk?) and translucency + SSS will work like there is a thin layer of "skin" and tiny particles underneath (grape?).
