Not just for protection of the pendulum. The concept is to match a circle within a circle. The Glow Guard being within the circle of the peep hole with minimum air gap between them, then place the pin on the target. This action becomes instinctive and provides quick to accomplish consistent aiming. Unless one is stacking arrow upon arrow, everyone will experience a decrease in arrow grouping diameter and a lot fewer stray shots that one just never counts as a good shot.
Most people think that only one eye can be used when using a peep sight.
This is because most everyone that has tried, incorrectly chose the wrong of the two images of the pin. The remedy is to briefly close the non-sighting eye, establish the guard inside the peep as previously described, put the pin on target and open the non sighting eye. The sighting eye will maintain the proper alignment of the peep, the Glow Guard, the pin and the target. The non-sighting eye will pick up the light image of the target and binocular vision is being used. And that is very important to us humans at low light.