When shooting a magnified scope lense in an adjustable target sight, often times it is difficult to get the target clear once it is magnified. So guys will use a peep sight that allows you to screw in different types of lenses inside them to help clarify the image through the scope.......it allows me to specifically pick out a spot on the target and see fine details through my .5 diopter (approx 4 power) scope. This setup would only benefit a target shooter......not a good option for a hunter or casual back yard shooter.