Thats a very good question. I am by no means an expert on this stuff. I am just stating what I liked and noticed since I started experimenting with different peeps.

I think the one thing that the peep really has going for it is the fact that you dont have to angle your head in toward the string. It just seems more natural the way the peep is configured outside the string. I tried going back to a regular style, but really had a tough time. It just felt unnatural to me.