Maybe this thought problem will put matters in perspective.
Being a engineer-y kind of geek, let's say I weigh my soap before and after my bathing. I determine the soap weighs 5 grams less per shower. (Based on a 140 g bar of soap, 30 days of use, 1 shower per day, so 140/30 = 4.7 g) Let's also say I take the bar to my soapy science lab and determine the soap is superfatted with a true 10% fat excess. I break out my trusty calculator, pencil, and paper and determine the 5 grams of soap with which I bathed contained a total of 5 X 10/100 = 0.5 grams of fat.
If I were an overly optimistic sort, I might assume every molecule of that fat happens to stick to my skin. Knowing what I do about how soap emulsifies fats to make them water soluble, I know only a fraction of that tiny amount of fat actually sticks to my skin. But I'll stick with the overly-optimistic view that it all sticks.
According to
Cornell University, the surface area of my skin is about 1.9 square meters (m2). The amount of fat on my skin is thus 0.5 g / 1.9 m2 = 0.26 g / m2.
A quarter of a gram of fat on 1 square METER -- that's about 1 square YARD for us Americans. (See SaltedFig's photos below for how much cocoa butter weighs 0.26 grams.)
Let me compare this to using my favorite lotion. I use 1-2 tablespoons (0.5-1 ounce or 15-30 grams) of lotion on my skin after showering. The lotion contains 15% fat, so at a minimum I am applying 15 grams X 15 / 100 = 2.25 grams fat to my skin. That is 2.25 / 1.9 = 1.18 g of fat / m2 of skin.
At least 4.6 times more fat ends up on my skin from the lotion than from the soap. Which one is going to make my skin feel more conditioned and soothed?
Bluntly, the idea of superfat doing amazing things to one's skin doesn't hold water. Superfat enough for safety and to ensure the soap is not overly drying to the skin. For the best skin benefit from the fats themselves, however, put the fats in a lotion or balm where your skin can really enjoy them.