"they do shift about 20% of impact away from my knees and toward my lazy arms and shoulders. Also with a pack on an incline they improve my posture, and balance, like a quadruped 4-legged animal or a hi-performance sports car taking on a corner at high speed."
Roger, you nailed it, exactly right. When I use them right I feel like a 4 legged animal, not a 2 legged person with two sticks in my hand. Proper pole length for the terrain, up, down, rolling, flat, seems to really be a big deal, I found myself dropping them bit by bit on my last trip, and certainly a fixed length pole would not have worked as well, nor a pole without straps.
I started using them recently, but always used a hiking stick, I like the balance of 2, and so does my back.
The sad thing is, they really do help your knees, but that help is best applied before the knees get weaker and damaged than after, but after they are amazingly helpful, my feeling is it's more than 20% of impact removed from knees, but I can't say for sure, it just feels like more.
I could see not liking them if you tend to hike pretty flat or rolling terrain, but we don't have much of that where I go, so that's not an issue.
there's also some interesting stuff I noted on my last trip with how your arms move, or rather, don't move, when using them, compared to the normal walking gait.
I am starting to suspect that growing up cross country skiing taught my body something about stride with poles that might not be as easy to do as one might think, I know when I get into the stride, my body recognizes it right away as something totally natural and correct. And when I go fast downhill the four legged thing, or crab, however you think of it, is very cool, faster with less traction on shoes, especially relevant with trail runners and their more slippery soles, not as deeply lugged, that is.
Now to get a tent that uses trekking poles to set it up, since I know I'll never go without them if I can help it.