Tying my own leaders lately, and learning a lot about leaders, I found this particular thread inspiring and very useful. Lately, the video from Tightlines Productions , https://vimeo.com/channels/patterns/91408485
, and a show on the Harvey leader on Eric Stroup's outstanding subscription fly fishing video series, Face Time Fly Fishing, got me great results just by tweaking leader design streamside.
My wife and I were fishing a western Pennsylvania creek with four weights. She was nymphing and I was fishing wets. Each of our hand tied leaders were tailored to our particular approach. Gorgeous needed a bit more turnover when she went to a Tungsten Torpedo and mini-bugger below a thingamabobber. Using what I had learned, I shortened up one part of her terminal tackle by about twelve inches and, just like that, her leader set up turned over beautifully. (And soon she had the delivery and drift she wanted and was into fish on the Torpedo).
I am slowly learning how important the leader is to casting, WAY more important than I had thought for years!
There is much, much more to learn, but just being able to "dial in" her leader was very satisfying and cool.