In response to Sun Ray's reply: They soften the "jarring" on the downhill. And they spread the load to the upper body on the uphill. They do slow me down a little - on even terrain I will carry them and not use them.
I have not had a "5 ice pack hike" since I started using 2 poles. I remember some hikes before the poles when I would come home and ice my ankles, knees and back.
Most people do not use poles properly. I adjust them for uphill and downhill which also slows me down a little. On long downhill stretches I make them a little longer and I shorten them for long uphill stretches.
I do remember some soreness in my triceps as I adjusted to the poles. And I remember a hike with some tightness in my upper back and neck after about 14 miles.
There are hikes where the poles get in the way - coming down Flatiron and Brown's Peak come to mind. But there are hikes with creek crossings or scree where they are indispensable.
The poles are a constant reminder that I'm not as young as I used to be. But they help me to keep hiking. Some day maybe I'll have to hike with a walker, but until then the poles do the trick. Rim to Rim at 90 in 20 hours with a walker? - that's ok, I can live with it.
The most important thing with poles - - make sure you have someone to carry them for you when lightning threatens
