This quote is suggesting that when it comes to the practical art of war, it is better to conquer the enemy’s country rather than destroying it. The idea is to take it over in a way that it is still in good condition and can be used by the conqueror. Taking the enemy’s country in good condition is more beneficial than completely destroying it. This way, the enemy’s resources can be used by the conquerer, rather than having to rebuild or start a new country from scratch.