I never leave home w/o at least one trekking pole whenever I'm hunting big game or scouting for same.
If I'm back packing or carrying a heavy load, I carry two.
"Carrying" doesn't necessarily mean I'm using it. Often it/they are simply attached for those areas where I'll need it. But "areas where I'll need it can mean any steep climb and always a steep downhill. Snow and ice are other conditions where they are needed.
With a bad knee, I would not just carry at least one, I'd probably use two. E
