When planning my traverse of the Glyders in 1996, I was so concerned about descending the steep scree path off the north side of Glyder Fawr that I bought a single walking pole to assist me. Two years later the tip broke off the pole during a walk, and I replaced it with not one but a pair that I have used on every backpacking trip since then and on most of my day walks as well.
From day one it was noticeable that my legs and feet and associated joints ached less at the end of a long walk, while the poles have also steadied me and prevented me from tripping or losing my balance on a number of occasions. Additionally, they are invaluable for crossing streams and there are other uses such as pushing overhanging vegetation out of the way as one passes. If I now go for a short casual walk in the countryside without the poles, I find my legs and feet getting a bit tired after a mile or so and I wish I had my poles with me.
There are some occasions when poles are more of a hindrance, the most common of which is when walking on a narrow path in heather and bilberry or long grass, when the poles catch in the vegetation. The best solution then is to use one pole only, or to use neither and just hold them horizontally under your arms, until the path improves.
Crossing stiles isn’t too bad, especially as you can reach down and plant the tip of a pole firmly on a step to steady yourself as you go over the top, but using ladder stiles with walking poles is deadly, here they are a positive hazard. You can climb the stile with the poles dangling on their straps from your wrists (the same as you must when there are any scrambly bits in a path), but when you are at the top and attempt to turn round to descend the other side they get in the way and threaten to trip you; this is not helped by carrying a heavy rucksack that affects your balance at the same time. The safest thing to do, I find, is to throw them over first, and then climb the stile without them.