The issue of residue on any textile should always be a concern. For those who are "encapping" office chairs, perhaps this isn't such a big deal. I can better understand cleaners' concerns when we consider "encapping" furnishings in the home.
A few of my own thoughts, which argue both sides of this issue.
1. How sure are we about the residues we leave, regardless of our method? I continually see cleaners overloading fabrics with prespray, scrubbing it in till its fairly wet, then they use their "dry tools" to extract. Think about that: They use tools designed NOT to wet out the back of a fabric to rinse out something they soaked INTO the fabric during preconditioning.
I am not feeling very good about the residues of d-limonene, butoxyethenol, surfactant, GKW, etc that is left when that's done.
2. How much residue does "encapping" leave? I did a test where I used a mist and brush technique on synthetic fiber fabric furniture, then wet vacuumed and vigorously towel dried the fabric. Afterward, I applied a water based fabric protector made for upholstery. It worked just as well as a matching area that I cleaned with a prespray and rinse method. A third area that I cleaned by using an upholstery shampoo, followed by wet vacuuming and toweling, followed by protector, showed zero water and oil resistance.
That test wasn't scientific at all, and wasn't used on absorbent natural fiber fabric. That's a test I'm going to have to do.
3. Given any choice, I'd rather rinse as much "stuff" (both soil and cleaning agent) from any fabric at any time, for a myriad of reasons. I don't see using an "encap" product as a preferred way of cleaning upholstery. I am looking at it more and more as an available method depending on circumstances. We are always forced to make "Solomon-Like" decisions when it comes to preventing browning/bleeding, getting things clean, getting them done in a reasonable amount of time, etc. What we decide in the end is a balance of economy, financial risk, and conscience.
4. "Wisdom from Mikey" Back when Haitian Cotton was a big problem (and there are still some raw cotton fabrics out there that behave very much the same), many cleaners used dry foam cleaning with a formulated Haitian Cotton shampoo to safely clean the fabric. I remember when I first came to know (though perhaps not yet love) Mikey, he said something that I have repeated in every upholstery cleaning class I have taught:
"One thing you can say about cleaning with Haitian Cotton Shampoo. You can guarantee that the fabric won't resoil......That's because once you use the stuff, the furniture will stink so badly that no one will sit on it again!"