One advantage is that you can fish far away from your position. If the fish are downstream of you and the water is too deep between you and the fish to wade close enough to present the flies this allows you to catch those fish.
I don't want to freeze!! Since I can fish at greater range I don't have to wade as deep. The last time I fished I didn't wade past my knees. This makes for a comfortable fishing experience
when the fish are are in water that is barely moving I can fish to them easily. I just use a size 8 or even ten shot. Also, in these situations. Where there is little to no difference between surface and bottom currents, I can suspend my nymphs. With long leader techniques you would have to constantly have to keep lifting your flies off the bottom because there is nothing to stop them from sinking.
That should be enough for now! Frank it's about versatility, you can't be a "one trick pony" and be a good angler!