Hi Geoff
I was keeping my reply generic, without any reference to specifics on the points I raised. I wasn't praising multi jet wands, merely pointing out some of the different characteristics.
As you suggest, many rinse/extraction machines have surplus psi so that the rinse can be adjusted to suit the needs of the particular application. But regardless of the equipment, energy (and heat) will be lost between the jets and the carpet. The shorter distance of travel, the less the loss. Also, to work with a higer psi on a single jet wand could lead to greater water consumption, so more down time with a porty.
Alan and Mike have also introduced valid contributions to this topic. The wear rate of jets (esp. plastic and brass) and the spray pattern, and also the smaller jets offer better atomisation (ie smaller droplets) for a more efficient rinse. Well that's the theory anyway.
And yes, I do frequently work with a cold water rinse, but this wasn't relevant to this debate. But today was a classic example of using cold. Large house, 4 bedrooms but I wasn't cleaning the H/S/L, on 100ft of hose. If I'd used hot water, I'd have had "pressure " marks on the H/S/L from the solution hose. With cold water, no problem. It wasn't practical to sheet the very long hall and landing.
On the furniture front, your risk assesment (yes, we all do it, usually without thinking about it) will always tell you if it's safe, for example, to move that 6 ft long sideboard loaded with antique china and glass, or whether you should just clean underneath. Same goes for office desks, some very large beds etc. etc.
Safe and happy cleaning
Ken