I bought a pair when recovering from a knee injury not so long ago. Didn't think much of them before but I really like walking with poles now.
Knees a lot better so don't bother day walking with them but always use them backpacking. Even on the flat they give you an extra kick. I thought my arms would get tired but not a problem. Balance is another area they help and save you energy, especially later in the day when you are feeling tired.
I never adjust mine except when setting up with my tent. Have them set at 125cm. If the track is narrow, I carry them in my hands. Rock scrambling they are a hindrance but overall, I think I can walk further with less effort using poles.