Fly fishing requires a leader line because the heavy colored fly line used to cast lightweight flies is too thick for tying on small flies and is immediately recognized by fish. When I fly fish for trout, I normally use a 9-foot leader of 2- or 4-pound fluorocarbon line. This is strong enough to withstand the strain of a large trout while still being flexible enough to float downriver if the fish spooks its prey. The best kind of leader to use with fluorocarbon line is one that is not too stiff. If the line feels rigid when you pick it up, then more line will be required to make your fly look like food. A slightly flexible leader that is not too thin or thick works best. You can buy pre-made leaders or make your own from braided fishing line. Trout are sensitive predators. They want nothing more than a chance at taking a tasty meal so they will often ignore anything that does not smell or taste like food. This means that if you were to catch your first trout with a bare hook, then you would probably just throw it back in the water without even thinking about it. However, if you did happen to catch a beautiful rainbow with a plain old brown hook, you would probably feel guilty enough not to do it again! The point is this: unless you plan to eat your leaders, there is no reason to use hooks on them.