The original purpose was because of GET raiders. Specifically, when Monster tried to take the 77777 and failed, they deleted their thread as soon as they noticed they missed the target. We wanted to prevent that, so we installed that feature in case the sane was tried on the 88888. It defaults to turned off, and is in fact off on every board except for /vx/, where it is on for reasons pertaining to that board. All posts on mlpol, sp, and every other board except vx, that are deleted by the user are automatically permanently deleted.