Kevo is right on the mark: it is always a tradeoff between better lure action and more strikes on lighter line; versus less margin for error when a big fish hits, you are fishing a snaggy area, or your line gets damaged. Very light mono on braided rivers will result in many unneccessary lure losses – which can get expensive. Stone bruises and nicks in your line can greatly weaken it resulting in lost fish; especially when a big one takes the hook. Fishing 15 pound mono is a safer bet when targeting big searun trout on an eggbeater reel in the lower Rakaia River as you never know when you might get a salmon! I always fish 6 lb mono in lakes and smaller streams. I should add that some blokes are “experts” at loosing trout lures. If you are one of these guys you might be better to fish heavier lines until such time as your lure loses reduce to a level more acceptable to your pocket!