This card can be useful when your opponent activates "Mirror Force". That way, your attack position monsters will be switched to defense position, avoiding the effect of "Mirror Force".
This card can also work great with "Tragedy". When your opponent's face-up monsters switch from attack to defense, every defense position monster on your opponent's side of the field will be destroyed.
Use this card to counter "Number 54: Lion Heart" whenever it's attacking, as it will most likely use its damage reflection ability to damage you instead. That way it'll shift "Lion Heart" into Defense Position, not only stopping its attack, but leaving it vulnerable during your turn, as ALL it's abilities only work while in Attack Position, including its immunity to destruction. Unless the opponent has a "Number Wall" active, you can effortlessly take out "Lion Heart" on your turn.
Use this card to simply prevent your opponent from attacking during their turn. If all the monsters your opponent controls are in Attack Position, this card can switch them to Defense Position, thereby preventing them from attacking during that turn, giving you a chance to counterattack safely.