It might be a good idea for a player to knock and try to end the game before their opponents have a chance to catch up if they have several completed melds in their hand & only need new rammy appone or two more cards to go out. Nevertheless, it could be preferable to keep drawing and discarding until a player has a stronger hand if they still have a lot of unmatched cards in their hand & are far from making any valid melds. It takes careful evaluation of one's own hand & consideration of opponents' progress in forming melds to determine when to knock.