The only danger associated with wearing a foreskin retracted is paraphimosis which occurs if the foreskin is too tight. If it is, it can get stuck behind the glans and cut off the blood supply to it. Never having had a tight foreskin, I couldn't say for sure, but I would imagine there would be a lot of swelling and pain long before it turned green and fell off so a guy would know that he needed to do something about it - like get to an emergency room quickly!

The folds of the retracted foreskin do need to be opened up for further cleaning as smegma can collect there even when the foreskin is retracted. This would be particularly important if the foreskin is very long.