Having had various athletic injuries in my youth, poles take enough pressure of my knees and back on the steep downs to allow me to continue to hike fairly aggressively.
Hike your own hike.
As others have stated, poles help you move faster in tricky terrain. I know that without them I would make much poorer time on steep ups and downs. If your ankles aren't in tip top shape (mine aren't) they can catch you from going down, and rolling your ankle in the process. In leafy terrain you never know what rocks, roots, and slippery mud pits are hiding underneath the leaves. I think I move about 50% faster with my poles than without them.
I think the best thing about poles is that they let you look up more. I spend more time looking at the scenery and less time looking at my feet, because I know if I misstep I can catch myself on my poles.
Poles do take time to get used too. If you've done nordic (cross country classic) skiing it'll give you a head start. But you may have to focus on where you're putting them for the first couple days.
+1
I never used poles and didn't feel a need to. One day, I was feeling frisky and bought a pair of Leki's. Let me just tell you, my poles are by far the best investment I have ever made towards my gear list, hands down. I am young, agile, in shape (somewhat ) and still feel like they make a world of difference.
The first time I used poles I was AMAZED by how fast I could move and rock scramble (and I live in NJ, so its allllll rocks). I move much faster, maintain a better pace, more agile, less blisters, easier on your body, etc. Plus, I can use them for my tent.
Also, anyone who says that using a wooden stick is the same thing, you better get yourself a pair of good poles and go try them for yourself.
And the reason that people with poles push poles on others is because we know the extreme benefits to them and we know that they work, just trying to spread the love around!
Smile, Smile, Smile.... Mile after Mile
I could come up with 25 reasons to bring hiking poles and only one reason not too, and that's weight.
I bet you theres not another piece of gear that you could list 25 benefits from.... try it.
Smile, Smile, Smile.... Mile after Mile
I do like my trekking poles, as everyone else has said, especially on the downhills and fording streams. I had one less expensive pair with shocks (Sojourns) but ended up picking up some locking Black Daimonds, which I really like.
I also use them on my hammock tarp in all but the worst of weather. Would not think of backpacking or dayhiking without them.
HYOH, YMMV.
The most exciting phrase to hear in science, the one that heralds new discoveries, is not "Eureka!" but "That's funny..." Isaac Asimov
Veni, Vidi, Velcro. I came, I saw, I stuck around.