We cleaned from the mid 70's until the early 80's with high heat truck mounts, an alkaline emulsifier (first one we used isn't made any longer; the last few years it was Dry Slurry). We had prespotter when needed.
To be fair, back then we were cleaning dirt colored carpet (brown, rust, olive green for the most part).
There is something to be said for the fact that if you can clean with a pass or two and no prespray that the carpet will dry quicker than if its heavily presprayed with an in line sprayer, then rinsed.
