That's also a great point. With traditional intelligence, it's unthinkable to sail your army far away to land right next to the enemy capital unless you vastly overpower your enemy anyways. With spying, you know where to land without a loss and when to do so to prevent the enemy from being able to retaliate, offering the deadly possibility of landing safely and rushing to the enemy capital before they can react. You can often then even start a takeover of their capital...
I don't think that is what he talking about. Finding a region without militia to land in isn't that hard, but if your enemy shows up there with their army, you will be slaughtered on landing.
