I was required to carry one when I was on the deck force, and I still do.

To actually use it on deck is an admission of poor seamanship. Line should be tied in such a way that it is easily untied. It is expensive, and cutting it usually ruins it, since the piece you are cutting is either as long as it can possibly be for a very good reason, or just the right length for its purpose. Either way, it is a shame and a waste to damage it. There are exceptions, of course; when trimming frayed ends, or damaged, weakened pieces, you have to cut.

But in an emergency, when you have to cut a line, you have to cut it immediately. You must have a knife on you, it must be sharp, it must be sheathed in a way that it is secured from loss, safe to carry and quickly accessible. A knife is one of the two basic tools: inclined plane and lever. It allows one to apply all the body's strength at one minute spot, magnifying it and directing it. I yield to your skill on the trail, but I won't go into the real world without one.