I never used a peep, life happened and I was kind of forced to quit hunting for a number of years. I bought a new bow a few months ago, set it up without a peep and my older eyes didn't adjust to well. I used to be able to line up perfectly with the left side of the string and could shoot really good. This time round I couldn't tell the left from the right everything is just too blurry up close. My vision from a couple feet in has changed since the last time I had bow hunted. I ended up putting a peep on this bow a month or so after I got it.
A friend of mine about my age had to switch from a recurve to a compound last year because of a wrist/hand/health issue. He went without a peep on his new bow and said he got real comfortable shooting after a slight adjustment period, he was money at the range.
He called a couple weeks ago, he had a big 150+, 8 point whitetail come out at his stand, drilled it broadside at 15 yards and when he went to retrieve it, he found guts on the arrow. (he thought he made a good shot) He evidently ended shooting 6 inches (left or right, I don't remember that part of the story) from where he had aimed. Fast forward a few weeks, he had what was the biggest deer he had ever seen come out at his stand, he said well over a 180 inches. The deer was quartered away, close shot and he shot it in the hind leg, missing about 6 inches to the same side as before. Lost both deer, the big 8 point showed up on a trail camera a couple weeks later, but he said it was sickly looking.
He called me feeling like crap, I told him my new issues with peep sights after he mentioned not using a peep, he actually consulting me and another friend of his that doesn't use a peep prior to setting up that bow. Anyway, he seems to think he looked on the wrong side of the string. Once you get over 50 your eyes aren't what they use to be.
Without hijacking the thread, there is a whole ethical discussion mixed in here as well.