JES II,
It means that an L-Wedge will outperform a 7-iron or 4-iron every time.
The firmer and faster you make the golf course the more the player hitting an L-Wedge has an advantage.
And, if you grow the rough high, the player trying to drive the green who misses has a clear advantage over the player who lays back and misses the green with his approach, and, the long player may very well have an advantage by hitting his L-Wedge from deep rough as opposed to a 7-iron from the fairway.