The idea is to desensitise the head to make it less sensitive, i love cut guys who moan, as they think they are missing something when they are not. When you have skinned back for a while, you may wonder, you still cum without issues. some like the look without being cut as well. I have done it for so long my head and skin has no feeling, but i can still push the skin forward
Well I still have plenty of feeling in my foreskin and head and I'd certainly miss it if I lost it.
Think of your hands, if you use them to work out in cold, the skin gets thick and tougher, but you still have all the nerves, you can still feel things in your hand.
Now imagine someone who has an amputated hand. They can touch and feel things with their stump, but it won't feel to them like it did before, feeling things with their finger tips, because all those nerve endings have gone. The same is true for a circumcised guy, they have feeling in the scar where the cut nerves now end, but they have none of the most sensitive nerve endings located in the ridged band so they can't feel the same kind of fingertip like touch.
It must be especially bad for guys that have all the inner foreskin removed and just have outer foreskin attached just under the head. It must be like us using the spoon method of retracting, but never being able to reverse it and expose the inner foreskin again.