When we run in trails, runners sometimes use poles unlike city running.
The largest benefit is to make us easier to climb up on the steep routes. It’s like climbing uphill with four-wheel-drive, as planting them in front of you provides balance and guidance. It means runners can climb steeps more quickly with, than without these poles.
If you’re using trail poles and your arms/back/shoulders to help you up and downhill when it gets tough, then your legs will be fresher for longer than if you hadn’t used poles.
Poles help us more easily find a sustainable pacing and step rhythm that runners can maintain for long stretches.
On the other hand, poles mean two more relatively large pieces of kit.
We just use poles on the steep climbs and descents. So you have to either carry them or pack them away when not using them.