Sometimes, a forum member creates a thread that later on, no longer wants people to reply on them. So in order to get it closed/locked; they have to go all the way over to the profile page of a busy staff member to pm them. But usually, the staff aren't paying attention at the current moment, and the member's request has to wait a few hours. So, to make things easier and a whole lot quicker, why not add a button next to edit, report, delete, etc. That way the member doesn't have to wait for their request because they can do it themselves. Yes, they can delete the thread, but maybe they want the thread to be a simple comment to all of a forum and not a huge discussion. And sure, maybe staff can close the thread themselves if the thread renders useless or inappropriate.