Poles are helpful at all times on the hiking trail but only if you've learned how to use them correctly and taken the time to practice using them. I'm not sure of the value of buying poles in SJPP, for example, and using them the first time on the stage to Roncesvalles. Many walkers on the camino use poles perhaps because they think they're supposed to use poles, but their arrhythmic tapping, randomly placed tips, and oddly angled poles show they're not benefiting at all but are simply carrying them.
If you use straps correctly, you won't use your hands to hold the poles; the correctly placed strap around your wrist allows wrist, arm, and upper body strength to work as a unit to push the the pole against the ground to propel you forward. Your very loose grip serves as a kind of stop to keep the top of the pole from moving about, but your hands does none of the actual work of pushing off. In addition, if you use the straps correctly, you will not risk breaking a bone in case you fall forward onto your hands, a fear that is often expressed in this forum when the topic of poles is discussed. I recommend this video as on using straps and poles:
How to Use Trekking Poles (Like a Boss)
I use poles for hiking just like I use poles for cross-country skiing, following the Nordic style. I can't imagine that even those who doubt the value of hiking poles on flat ground could see themselves (or anyone) cross-country skiing without poles. Poles propel you forward on flat ground just as they do on snow, reducing the work of lower body muscles. The key is learning how to use poles and then practicing so that walking with poles becomes second nature; for example, I can adjust from flat ground to an incline and then swing the poles in front of me for a descent, all without losing stride or rhythm and all without thinking about what I have to do. But then again, I have used poles on every hike and every walk (even to the library) for the last 10-15 years.
High quality caps for the tips are an absolute necessity, and they make using poles on paved surfaces possible.
And in case anyone is wondering, I'm in my late 60s.