When your the underdog and you hold a pass that has defensiveness from terrain , attrition from terrain or both . Since the primary purpose of Scorched Earth is to drain the oppositions manpower or economy if they ' re using mercs , hiring a fort defense advisor ant sitting behind a fort in Fezzan or in the Himalayas can be a viable alternative to engaging the enemy armies , as you still accomplish the goal of diminishing their manpower . the wiki states that you can use Scorched Earth on provinces that you control , so I assume that you can use it on occupied provinces in war . This can be of situational use as Scorched Earth lasts for 5 years and also provides the maluses of 33 % goods produced and 50 % institution spread rate . Since Scorched Earth only costs 5 mil , you can use this to some benefit in the early game to cripple your enemies by weakening their economy quite substantially albeit at the cost of mil points , think fo unjustified demands though and by limiting the speed at which they can embrace institutions quite weak .