It's a very useful tool to have. Originally I carried a knife because I worked at a barn, we used it to cut hay bales open, feed sacks, saw dust shaving bags, etc... not to mention of a horse pulls back on the trailer and you can't quick release the halter, you have to cut the lead line.
Discussion
The applications are infinite. I go one boats all the time, so it's a given you'll be carrying something slicy. But on land I've used my knives as improvised tools to cut, slice, whittle, remove, scrape, hammer, crush, pry open... all sorts of stuff.