The Perfection Loop is an amazing knot for making loops on monofilament fishing line or nylon leader. It is strong, and makes a beautiful knot! Its small, and goes through guides pretty easily. It is a must have in the fisherman's arsenal of tricks.
I use this the most to make loops in leader that I need to connect to a loop in a fishing line. The loop to loop connection is easy, and strong. I have also heard that people use this knot for tying on flies. However I have other knots I find better for this.
Not only is this knot strong and effective, its also easy to tie. Once you get the hang of it, you can tie it in a few seconds. Being quick to tie and effective really make this an excellent knot.