"To each their own". Not to be contrary, but I take a little diff. view on trekking poles & why they should be inlcuded in a SUL / UL / LW 'kits'.
Trekking poles are not a new fangled invention. Perhaps in their modern form they are new, but people have used hiking staffs made from branches for as long as people have been around. They must have some benefit or they would have been discarded long, long ago. First order of business for my grandmother upon entering the forest was to find a branch to use as a hiking staff. These branches sure weighed more than a modern pair of CF trekking poles. It's not that she was elderly or infirmed, for even in her mid-70's, while on vacation, she climbed the Alps to a pick flower she remembered from her childhood.
You're absolutely right about needing to do more "work" when using trekking poles. You're also right that this is not the most efficient way to use the muscles of the upper body. This extra work can be minimized, however, by using poles of the proper length such that the hands, generally, unless ascending a steep grade, do not rise above the level of your heart while using the poles. Doing so places more load on the heart to pump add'l blood to a higher level, i.e. particularly your forearms and hands. This principle is readily grasped by anyone who has ever experienced an episode of orthostatic hypotension upon rising up from a reclining or seated postion too rapidly and experiencing a period of light headedness or even blacking out. [NOTE: You young'uns may not yet have experienced this, but live long enough & your chances become greater of doing so. I think keeping your cardio-vascular fitness level up will reduce this likelihood even with aging, but I am not a physician & so someone better qualified should perhaps comment on this point.]
Since even proper use of poles increases slightly the work you are required to do, how does using poles produce any benefit?
Please correct me if I'm wrong, but I believe the following are some of the reasons/benefits:
1) Increased stability - particularly on rough or uneven terrain. Even with NO pack, stability is improved by having a wider "base" which is one thing trekking poles do. Having a base as wide as possible relative to one's CG (center-of-gravity) produces more stability. This is true whether one has a heavy pack, light pack, or no pack. Is it Leki that has T-shirts printed with the words "Four legs good; two legs bad"?!!! Certainly the benefit is less noticeable on flatter/smoother terrain.
2) Redistribution of Workload: I believe, though I have no carefully controlled empirical evidence, only my own anecdotal knowledge/experience, that the redistribution of the loads and work, which would only be done by the muscles of the lower body, which is now possible through the use of poles has an overall benefit of being able to hike faster/longer and/or with less fatigue as muscles of the upper body are now being recruited to do some of the work. The net effect, even considering the slight increase in overall work being added by the use of the poles, is to reduce somewhat the work being done by the muscles of the lower body. Therefore, these key muscle groups will NOT fatigue as rapidly, enabling one to hike longer. How often have you seen someone ascending a grade press the palms of their hands on their thighs to "help" their legs by reducing the workload on the leg muscles?!! The tricep muscles of their upper arms & their lats & pects are prob. contracting forcefully to assist the gluts/quads in extending the upper/lower leg, respectively, as one steps up. Isn't this basically what trekking poles would do in a similar scenario. [The use of trekking poles vs. no poles might be a good senior project or graduate level thesis(???) for someone in any number of fields of study. Research would include both field study, plus oxygen consumption measurements to help determine workload/efficiency & electromyograms in a laboratory enviroment - plus many other technical methods of acquiring data. I for one would be interested in reading the thesis and learning something. It would be nice to have an empirically determined quantification of the redistribution of loads & work as measured in a laboratory experiment & any overall benefits that would/might result.]
3) With each step, I notice, particularly when descending steep grades, the stress to the lower joints is reduced when I use trekking poles. Just climb & descend a ladder wearing your pack. Try it once using your hands & a second time w/o using your hands. Which is easier on your legs & feels more balanced? Yes, the ladder has a steeper "grade" to it than most terrain on which poles would be used, but then again one isn't climbing the ladder for 10+ hours a day as one does on treks. If some benefit is realized during a short, more intense test, then perhaps a similar benefit is to be realized for a longer, less extreme hike. I hope this point is clear? Perhaps a better example could have been chosen to illustrate it? If you have one please share it.
4) For tarp & many tarptent campers (depending on the tarptent they are using), when trees/branches are not available for use as tie-off pts for guylines, instead of having to carry single duty poles for pitching their tarp (these also add wt. & increase the work needing to by done by the hiker, do they not?!), they can make their trekking poles do dbl-duty by also using them when pitching their tarp. Obviously, this point is only valid, if trekking poles actually serve at least one other useful purpose, which I believe they do.
5) Some trekking poles are fantastically light, e.g. GossamerGear's LightTrek & LightTrekPlus poles, & the BMW/BPL StixPro poles & prob. weigh less than sng. duty poles intended solely for pitching the tarp - and so, would then be a better choice for lightening one's full skin-out wt & base pack wt.. Even though these are fixed length poles, there exist techniques for joining them together if a longer support pole is req'd for pitching a teepee or pyramid style tarptent which req. a single center pole [NOTE:The stiffer one piece poles would be a better choice for these long support poles since they have less flex.], as well as techniques for preventing the guyline from slipping down the pole when used with flat/shaped tarps and the pole happens to be too long. Heavier, adjustable poles are NOT mandatory for tarp campers. What I've just written is NOT first-hand knowledge & perhaps someone who tarp camps w/fixed len. poles should be commenting on this point.
This post is gettin' a bit long winded, so I best stop here. Hope someone else will continue with any other benefits of trekking poles I failed to mention and why they should be included as part of a SUL 'kit'. 'Nuff said.