A metal filing cabinet full of files is one of the heaviest things per cubic foot in an office. Emptying it or at least locking the drawers shut is the difference between an easy move and a crushed foot.
Pro tip: If you cannot find the key, run several wraps of stretch wrap around the closed drawers to hold them shut.
Watch out: Never move a filing cabinet with a top drawer open or loose; the cabinet becomes top-heavy and can tip onto you.