ORIGINAL: archer 2
For all the reasons Jeremy stated,not sure about the weight difference between nock and string loop though as I have never weighed them. One other reason is that with a brass nock over time and shooting can tend to cause the string fibers underneath the serving to sever.
The loop weighs slightly less than a single brass nock. Then you add the eliminator button that is needed, it is roughly twice the weight of a rope loop. With my short draw length, I try to find speed whereever I can.