Below is an interesting video demonstrating how to tie a perfection loop. A perfection loop is a great way to give your streamers and wooly buggers a little bit better action in the water. They allow the eye of the hook a little more freedom from the tippet in the water. A clinch knot holds tight to the eye of the hook and will restrict the movement of the fly. But by putting a little air between the tippet and the hook eye a perfection loop will let your fly wiggle just a bit more which will translate into more strikes.