You can only activate this card when both you and your opponent each have 5 or less cards on the field. As long as this card remains face-up on the field, the total number of cards that each player can have on the field is 5.
This could be useful in certain decks. That limit space on the field. Bad card against GL beast, because they don't need much space to work with. But great start to early game limiter. It might be good in, making it hard for the other team to decide between trap or monster zone.One less trap or one less monster to use.