The Needle knot is a quick easy way to fix a broken loop on the water. Loop connections on sink tips and fly lines can wear over time, instead of trusting it, replace it with a new one.
Useful tip. You can attach a tapered leader to a cut end (no loop) of a fly line to give you great transfer of energy and accuracy. If you carry a simple needle in you bag you will always be able to continue fishing if you break the loop of your fly line or snap a poly leader or tip.