Editing a post removes the credits the post was worth, and re-adds the new amount the post is worth after the edit.
The original purpose for the credits is no longer available, but they can still be used for shop items, many of which are not currently enabled. All of it is just fun stuff anyway, with some customization options.
Some people also seem to be completely unable to earn credits from posting, and why, I have no idea. Have not been able to find a common link between any of the accounts that are not generating credits.