I’m curious. What does the second iteration accomplish? Is it dirt and grease that is embedded in your skin? What kind of job do you have if you feel comfortable answering?
It's not usually needed, but if I'm really sweaty and sticky the first washing removs dirt, and the second washing adds "squeak" is the best way I can put it.
It just feels cleaner. I assume it's because the additives in the shampoo become overloaded on the first use, and are active on the second.
I like the squeak too. I recently moved to a place with hard water and so everyone has water softeners. With this super soft water I can't get the squeak ever. It just feels slimy to me.