Carrara treats SSS just like most of the "big name" programs - it's all fake. Carrara is a Surface modeler as compared to a Solids modeler (the kinds of modelers used by industrial engineers/designers) Therefore, Carrara doesn't calculate internal disturbances from other objects/solids for effects like SSS. Things like Caustics and Refraction are handled a little differently than SSS because Carrara assumes that there is nothing inside an object so it simply looks at the value you've assigned for Caustics/Refraction and "bends" the light accordingly. To get an idea what "real" SSS would do to your computer on render, try creating multiple glass spheres inside of each other, all with different caustic, transparency and refraction settings, select Indirect lighting and render. When it finishes next year, let us know if it was worth the wait. ;-) The variables and calculations required to do "real" SSS are massive because you have to plan and manage different values through a solid. That's why it's faked.