Certain PIN codes are blacklisted on iOS. For example, iOS recommends you don't use 0000 or 0011, but doesn't have a problem with 0001 or 1001. But what combination of numbers are blacklisted, and ...
It may be useful to change the PIN code of a newly purchased iPhone (if the PIN is set to 0000 by default for example) or for safety reasons to protect from fraudulent use of your phone in case of ...