The rule with any weight rack is simple: it moves empty, always. A power rack or tree loaded with plates can easily exceed 500 pounds, and that weight is exactly what turns a tip or a slip into a serious injury.
Pro tip: Load individual weight plates into small, sturdy boxes by weight, no more than 40 to 50 pounds per box, rather than one giant box that becomes impossible to lift safely.
Watch out: Never move a weight rack with plates still attached; a loaded power rack can weigh 500 pounds or more and tipping it under that load can cause serious injury or crush a foot.