Leader lenght- What pound strength

This subject has crossed my mind, every spring, when I get the reels ready. and I set up the rods for the different styles of lures. Whether its a coated wire leaders, or bare wire, its still wire.If you were to cast Spinnerbaits, say1/2 - 3/4 ounce, would you use a shorter wire say 5-6 inches, and a lighter weight wire. Compared to a 9-12 inch leader for larger lures like Grandma and Jakes. Why is the length of the leader so important, for when you change to trolling , I tend to see some muskie fisherman using leaders of longer lengths, say-12-36. Would it not be better to have a shorter leader for trolling, so the muskie does not wrap up its self, and possibly get injured in the process. What say you muskie hunters out there? Wire or Mono? Short and light? length with might?