In my experience over five years and as many Caminos, I believe that there are three schools of thought regarding using hiking poles:
1. Pilgrims who cannot conceive of hiking anywhere, especially a Camino, without poles. I am firmly in this tranche.
2. Pilgrims who do not use poles and do not think them necessary.
3. Pilgrims who love poles, but ONLY if they are specifically "Pacer Poles." This is both a type and a brand.
In my first Camino, I learned to walk with poles in less than five-minutes. Once you do, it becomes autonomic, almost like walking in general.
As others have correctly stated, they transmit up to 25% of your rucksack weight through your torso to your arms. I do not understand it. But I DO know that it works...somehow. Using poles is, IMHO, like having four-wheel drive on an uphill segment. On downhill segments, it is alike have four wheel brakes.
As a general rule "GRAVITY SUCKS." It will seize every opportunity to pull you back down a hill when you are climbing, and to hurl you down a hill if your are descending. If you tend to be quite top heavy, like me when wearing a 12 kg pack, you can well understand what I mean.
There are shorter folks, with shorter legs and with pelvic girdles that are closer to the the surface of the earth. Seriously! Think about this. I have long-observed and watched who seemed to be making the best progress without poles.
It occurs to me that there is a geometric relationship between the distance, or height of one's pelvis & waist above the ground and one's relative stability over varied terrain. Year after year, I am in wonder over shorter pilgrims who can proceed like mountain goats even with heavy rucksacks, while I struggle to make way.
Anyway, my bottom line is that I am firmly in group #1 above. I could not conceive of doing a Camino without my poles. On my first Camino, my poles literally saved my life, preventing me from being hurled off a steep drop. Subsequently, I have found myriad uses for my poles.
Fighting off dogs is NOT, REPEAT NOT, an issue....period. In fact, when approaching dogs in Spain, I always lift my poles and carry them under one arm while speaking softly to the dogs telling them what good dogs they are, and to remain tranquilo / calm. It usually works.
I learned some years ago that rural dogs in Spain are generally farm dogs and are regarded like farm animals. Many rural dogs were raised and trained severely using a stick or cane to enforce discipline. Hence, the sight and sound of swinging, click-clack, of hiking poles causes agitation. I remove that stimulus by carrying my poles until I am "around the corner" and out of their territory.
Conversely, the folks who eschew poles do not use them because they feel they do not need them. That is their choice. I respect that choice.
As regards the pacer pole discussion, this is simply a difference in preference. Pole users who switched to Pacer Poles say they are much better and easier. Personally, I do not get it. But, again, that is their preference and I support it.
When considering poles, obtain the lightest variety you can afford. IMHO, Anti-shock poles are a gadget and a fad. They tend to break more easily under sustained daily use, and are harder to repair. They are also heavier.
Most good hiking poles are made of aluminum alloy segments. The segments adjust using either the classic twist tension fasteners, or a cam-lock arrangement, or a combination of the two. Most poles use the wist tension system. The components are somewhat generic and repair parts can be found along the way. I have also fixed slipping tensioners with duck tape. Keeping it simple is a good rule to follow.
Carbon fiber poles are VERY expensive and I recommend them only for folks who are prepared to pay three to four times the price of a good aluminum pole, and who have used poles previously. I used Leki aluminum alloy poles for four Caminos before stepping up to carbon fiber. The carbon fiber poles are lighter than the aluminum and collapse small enough to fit in any rucksack or piece of luggage.
Beware of buying poles in a souvenir shop in Europe. Just remember that you get what you pay for. This said, the Decathlon chain of sports department stores across Europe offer very good value for money and their poles can be seen all up and down the Camino. Check out
www.decathlon.es to locate your nearest Decathlon in Spain.
I hope this helps.
Seriously, I wanted to keep my arms in shape, and didn't feel like doing push-ups at the end of the day. 
