With a SSS map you can decide where the “light” should be abel to pass through the mesh/texture -> with “opacity” you can control the strenght of the SSS effect. The best way to see this effect is, when the sun shines on the mesh from the back side 
With a SSS map you can decide where the “light” should be abel to pass through the mesh/texture -> with “opacity” you can control the strenght of the SSS effect. The best way to see this effect is, when the sun shines on the mesh from the back side