Susie makes a good point, well more than one really. But the one I want to address is the condition of ones skin whether clean or dirty. Some of us have skin that is more delicate, while others have skin that is tough and capable of withstanding harsher treatment. And many other variables of skin condition exist. So how much SF is in the soap is only a part of the components that affect how ones skin responds to a particular soap formula. It's not all about the dirt and grime or dirt and germs or dirt and oils we may or may not to remove from our skin when we wash. It's also about how we want our skin to feel after we wash. (Besides being clean.)
I don't want my skin to feel like I just washed with sandpaper and be reluctant to rub my hand across fine fabrics for fear of snagging a thread because my skin is so dried out from a harsh soap that it snags threads. Now, many will say that soap doesn't moisturize and yes, that is a valid statement. But the skin feels as though it is moisturized when the soap doesn't strip it like I was trying to refinish furniture. That's what I'm after, as little disruption to the skin's acid mantle as possible. Since making my own soaps, I have found that most of the time I don't need to apply skin moisturizing lotions, etc. So I know I am achieving a better soap for my skin's condition than I had before when buying the soap I used to use for many many years.