When your descending down a very steep mountain with a load of meat and gear or crossing a scree field, trekking poles are worth their weight in gold. I always carry 1 and sometimes 2, I don't use it all the time but for the times when I do need it, I will have it with me. Your knee's will thank you for it.
Forgot about that one. Eccentric contractions like a downhill descent are what do the most damage to muscles and tendons.
