Why? For the obvious reason. Though I've never had to use it on the trail yet. I just hate the thought of being out somewhere without it when something gets stuck in my teeth. Trail food often includes nuts and nuts are notorious for getting stuck between my teeth. How annoying.

Aren't you glad you asked?!

I am, however, convinced that at some point it will save the day for me or someone--somehow, somewhere. It's strong stuff and could come in handy during an emergency. A friend and I once considered using it as a makeshift dog leash to help convince a lost dog to follow us. Someone else in the group ended up having a piece of real rope though.