I think learning to shoot with both a peep and a kisser teaches you to check more than one reference point at full draw. If you shoot with a kisser long enough, you can learn to shoot without a peep for better visability when hunting. Some say that they see well enough with the big peeps but can they shoot in the dark with a flashlight to assist like I can? If you also shoot with a kisser only long enough,, you can do very well also without the kisser! The peep and the kisser especially teaches you what feels right at full draw.
The problem with shooting with a peep and kisser with a moveable single sight pin at longer yardages is that you can feel yourself coming off the kisser to see through the peep as the sight housing goes lower on the long shots. That's when you can only rely on the peep to make the shot. To me it felt wrong at long range shooting so I had to choose which I was going to keep. For me it was the kisser because I found that I could shoot equally well without the peep and hunting is what I do the most of. Long range practicing for hunting is my only other concern.