A knife can be an invaluable asset in all kinds of situations. However you must remember that knives are dangerous, and can be weapons. Safety should always be of paramount importance. No-one (and this includes leaders!) should be allowed to carry or handle a knife unless they have proven their competence to an experienced instructor. I would not allow scouts to carry knives on their person at camp all the time, only when the activity specifically requires the use of knives. I would certainly never allow anyone to carry a knife on their person off the site, there is simply no need for it. Off site the knife should be safely stored in your backpack.
Remember you are only as sharp as your knife. You must keep your knife sharp ready for use, a blunt knife is a dangerous instrument and an inefficient tool. Don't misuse your knife. Never throw it into trees or the ground. Keep it clean, and if you don't intend to use it for a while, oiled and in its sheath.