So I'm not alone in being skeptical and puzzled.
The usual default of 5% superfat seems to me to be a more useful starting point for most recipes. A 5% superfat starting point has fewer exceptions to the rule than this other idea.
For example, the "1/2 of cleansing" rule would say we should be using a superfat of 33% for a 100% coconut oil soap, rather than the 20% superfat that many people use. It would say one should use zero superfat for a 100% olive oil soap. Neither makes sense to me.
And, yes, Ali -- even for a more middle-of-the-road recipe, it's going to call for more than double the superfat than the 2-3% that you and I use.