Thanx for the clear explanation. By the way, just found out that sss slider can go beyond 1 to increase radius.
But.
Unlike in a Physically Correct Rendering Research Laboratory, on actual cg production cases we often need a simple mix between sss and diffuse. Also, among lots of other things, we might need that sss anisotropy thing which got implemented and then scraped.
Artists often want to play with things, not do a mathematical analysis of light propagation on a spherical horses in vacuum. 
By the way, great gif, very helpful.