Mikey P said:
Soap Free has some Powdered Peroxide in it.
does Procyon?
Procyon is straight Sodium Tripolyphosphate.
MasterBlend's Soap Free is quite a bit more complex, as it is designed to be more effective than STPP alone.. In fact, Soap Free has more in common with traditional in-tank emulsifier detergents type products, with the exception of an actual detergent surfactant (which is the whole point behind using a "soap-free" product). MasterBlend's Soap Free also contains Sodium Percarbonate (affectionately known to BBS readers as "powdered Peroxide")
Soap free also has a component of traditional cleaners that Procyon is desperately missing, and that is a
Corrosion Inhibitor. STPP just loves reactive metals like brass. Using straight STPP without a corrosion inhibitor is no problem for us suppliers, as we make extra money when your brass fittings, your disconnects and your pressure valves fail ina fraction of the time they usually last.

But, if you are a conscientious cleaner who has limited financial resources, or you just plain like to spend your money on other things, you may want to think twice about using home brews or products that have corrosive components & don't also contain corrosion inhibitors. 8)
As to the original question.
If your goal is to rinse surfactants from carpet fibers (e.g. your detergent prespray), then Soap Free is not going to have much advantage over water. If you want to rinse better than plain water, then use a rinse aid product like
Hydramaster's Clear Water Rinse. It will make water rinse better, so you'll move faster, and use less water (enhancing drying, less over-wetting & less wicking, if that is your issue).
If however, your goal is cleaning, then MB Soap Free will run circles around plain water. The builder (STPP), the Percarbonate, and few other actives will actually clean soils, rather than just trying to rinse water soluble ones.