Hypothetical situation: I'm a moderator on the Truffles site. I'm very fortunate to have a user that is in the professional truffle-making business, and thus is very knowledgable about truffle science — he's a very valuable user.
However, this user also like to take pictures of truffles. Awesome, we love truffles. Not awesome: The guy also has employees. All his employee's social security numbers are posted in big letters on the wall right behind his truffle-picture-taking spot. So every time this user posts a picture, I have to go and edit his contributions to blur out the social security numbers and purge the history so that ordinary users can't find the original pictures on the site. This is very time consuming.
Really this boils down to: Someone is constantly posting things they shouldn't be posting and they need to be purged. They're otherwise a valuable member. What do I do?