Emulsifiers including Formula99, RSF Alkaline Rinse and others provide an extra boost of cleaning during the rinse portion of cleaning. You may want this extra cleaning power for more heavily soiled carpet in rentals, restaurants etc.
But there are some other good reasons to use an emulsifier. For example, you have cleaned the center of a room and now move a sofa away from the wall to clean the carpet that had been under the sofa. That carpet probably did not get any prespray. The soil is likely rather light, mostly dust. You could get your pump-up sprayer or disconnect the wand and attach your in-line sprayer to give that carpet some prespray. But all that might be needed is the little cleaning power of an emulsifier in the rinse water.
Another situation might be a heavily soiled traffic lane. You want to scrub this area with several wand strokes. After the first wand stroke, you have rinsed away almost all of the prespray. If you did not have an emulsifier in your rinse water, you would be making those extra cleaning strokes with just water.
Acid rinses have the advantage of neutralizing any alkaline detergent residues that remain in the carpet. This reduces resoiling. Any detergent left in the carpet continues to work or react with soil. When active detergent residue is in the carpet, it "cleans" soil off the bottom of shoes and this soil is now on the carpet.
Acid rinse products also leave the carpet feeling softer. This is important in residential settings where people might walk on the carpet in bare feet or just socks. They may even lay on the carpet or infants may crawl on the carpet. Those things are not much of an issue in a commercial setting unless you are cleaning a day care or higher end hotel.
Leaving the carpet in a slightly acid state can also make some protectors perform better.
Using an emulsifier and an acid rinse would cancel each other out. You would just leave more residue.
In the past, many cleaners would use an alkaline emulsifier in the rinse water and then spray on a mild acid after cleaning. Cleaners seldom take the time to do this extra step now.
Ultimate Fiber Rinse was developed to be an acid rinse that also has some cleaning power. For most residential carpets and sometimes other carpets as well, it provides the best of both worlds.
The newest development in acid rinse products is RSF Acidic Rinse which is a powerful cleaner but on the acid side to retain the ability to neutralize alkaline residues thereby slowing resoiling and maintaining the soft hand or feel of the carpet fibers.
Like many acids, RSF Acidic Rinse removes deposits and scale that have built-up in your hoses and other plumbing. If you have been cleaning with hard water, which can be a lot of loosened scale being cleaned out. This can clog filters or jets, so, run your water into a bucket for a while when you first switch to Acid Rinse. You will catch most of the loosened deposits. If you are continuing to use hard water, expect to see some white mineral deposits on the outside of brass connections.
If you are using hard water, you may prefer using Formula99 which also is an excellent cleaner and emulsifier but works on the alkaline side and does not “Descale” your plumbing while you clean.