In the given scenario of a large park with no discernable edges this solution would be efficient. The problems start to occur in smaller spaces when boundaries such as walls are present. In these situations there would be a lot of space lost at the edges with hexagonal packing and the conventional square packing is often more efficient. The edge effect becomes less of an issue above about 50 individuals though as the lost space becomes relatively less. So in a wide space with more than 50 people use hexagonal packing. If you're in a room a square arrangement is probably better.