[Kuritza]

Do as much damage as possible?

You know, there is a difference between resisting till the end, mustering your forces and trying to survive while you can... And just turtling in your castles and, say, sending black minions with bane venom charms without even trying to give a good fight.
There are different opinions about Burning Earth strategy; I think its rather unportsmanlike. Do your best to survive, make him bleed for every province he takes etc - but if you know you are dead, just die already and try to do better next time.
Others will disagree and say Burning Earth is very fun and fair. Who's right, who's wrong? I doubt there is one true answer.

Where was I...
Ahem, there are situations when going AI is a good thing to do. When you just know you dont have any tricks left (your God has died, your research is low, your enemies are well ahead of you), you can just as well let the AI handle your troops. AI doesnt mind micro-management, and he doesnt stale.