An experienced flyfisher once bragged he had used the same leader for an entire season simply by adding tippet as needed. His rod, reel, and line cost roughly $1300 yet he chose to economize on leaders. Really? The key to fooling fish lies in presenting the fraudulent meal in the most likely fish-holding location in the most natural manner possible.  Since the leader is a critical component of the delivery system it must be infinitely adjustable. The length of the leader must be customized to deliver the fly to the desired location. This could mean shortening your leader to 3 1/2 feet, for example, on a full-sinking line to prevent the fly from bowing back toward the surface rather than remaining deeper. Or it could mean extending your leader to 12 feet or more to allow a wet fly to be fished a little deeper without changing fly lines. Another consideration is that the suppleness of the leader must be adjusted to accommodate the weight and/or wind resistance of the fly. One leader for the season? That’ll work only if you have an aversion to catching fish.