I learned a lot about residues left behind by hot water extraction from that machine. There was a local business that I used to clean for training purposes for a few years. It was always hot water extracted, and I had used a variety of presprays, detergents, and rinses each time depending on what I wanted to experiment with or the customer intended to use in the business.
Then came the day John Downey brought the Steamin Demon for me to try out. When I rinsed that carpet (no prespray, just clear water) the amount of detergent that we pumped out shocked and embarrassed me.
The way I approach what I apply, and how much I apply, as well as how thoroughly I "rinse" changed after that.