I used a single pole (Leki hiking staff) for many years before switching (at my daughter's insistence) to two poles 6 years ago.

The difference was phenomenal--almost 100% improvement in hiking pace, balance, support for knees going downhill, lessened fatigue going uphill. The poles have saved me from a number of potentially serious falls.

I also use the poles (with rubber tips on the points) for exercise walking at home. Using the poles turns walking into a full-body exercise that really works on the core muscles.

I switched from aluminum to carbon fiber poles several years ago, and found another big improvement in lessened fatigue. However, I still use the aluminum poles around home and for dayhiking, saving the carbon fiber ones for backpacking. Both sets of poles are also Leki--I'm very satisfied with their products.

While the rubber tips help reduce damage in sensitive areas, and I have used them in high alpine areas, you definitely do not want to use them on wet rock!

On how to use trekking poles: "Pete's Poles Page" is the best site I've found.