I started using a single staff after busting up a knee, requiring extensive reconstructive surgery. At my daughter's advice, I bought a pair of trekking poles and have never looked back! They have been wonderful for my bum knee (and the other one which is not exactly 100% any more), have helped considerably with balance and have saved me from several potentially serious falls. They also hold up my tent at night. Other multiple uses are as potential splints or as a travois should my dog get hurt (only problem will be keeping him on the thing!). I even use them (with rubber tips on the ends) for exercise walking (aka Nordic walking)--they turn walking into a whole body exercise that works the body core muscles!

Lots of great stuff on trekking poles here.

Nearly all the long-distance hikers I meet (living close to the Pacific Crest trail, I meet quite a few) use them.

If you're dubious about their benefits, check thrift stores for a set of cheap ski poles of the right length and try them out for a while. Or get the inexpensive ones sold by WallyWorld.