Pulling back the foreskin or not

What happens if you don’t pull back the foreskin when you stretch or hang? You got stretch marks, that’s it’s all about?

Nothing bad happens if you do not retract while doing normal stretches, that is, if you do not hold a stretch for too long a period. 30 seconds is good. Holding for really long periods, I have found, causes darkening in the foreskin as will some girth exercises like “horses”.