I started using trekking poles two years ago at my daughter's insistence (before that I used a single staff). The poles have saved me from a number of potentially serious falls, and really help my knees on the downhill. I also use them for exercise walking ("Nordic walking"), with rubber caps on the tips, at home, since they convert a waist-down exercise into a whole body exercise that does great things for the core muscles. If I need to scramble (something I rarely do any more), I can collapse the poles and tie them to my pack. I also use them as tent poles, so they do double duty. They can also function as a splint or as the base for a travois should my dog be injured (the main problem being to persuade the dog to stay on the travois....) The poles are also a great place to carry that important essential, duct tape. In other words, a true multiple-use piece of gear.

As has been cautioned, though, poles shouldn't be used as a substitute for getting your leg muscles fit! You need strong leg muscles to support your joints and prevent injury, and the poles won't substitute. And you need to practice balance exercises (at least I do!).

It's a good idea to get the rubber tips for the poles even if you're not planning to use them on pavement or sidewalks. Unless you're on slippery ground or crossing a stream, where you really need those sharp points, the rubber tips will protect the trail from damage and also preserve the points longer.
May your trails be crooked, winding, lonesome, dangerous, leading to the most amazing view--E. Abbey