DP and I each have a set of Black Diamonds that are collapsible that we love. I use one (trying not to look too uncool) if the hike is 3+ miles and both poles (don't care how I look) if it's around 8+ miles. The past 10 years or so I noticed knee problems on descents during long hikes. A friend lent me her poles for a multi-day trek up Mount Kenya - don't think I could have made it without them. I've been sold ever since.