I run a shorter leader if fishing heavy-fast water or pocket type water. On average I run 30-36" leader. A longer leader will give your bait a larger radius to move around your weight, but that can be a bad thing if you're fishing a fast flowing 10' long pocket that's 5' deep and 4' wide . You may never get your bait down in time if you're using a longer 36" leader, it'll just ride up in the upwelling current or will not sink fast enough before you finish your drift. This is where an 18-24" leader would be best. There is no one best leader length for all applications.