To me extreme pillage == game over for that AI. So yeah I pillage after the start. You have to understand I expand aggressively at the start so I really typically dont want another city. Pillaging every square around a city is about as good as razing it with alot less damage to yourself. I mean you pillage half the AIs empire and that AI will never be a force again in that game.
Very true. I think a lot of people don't appreciate how devastatingly powerful pillaging can be. Working tiles is such a fundamental part of victory that losing hundreds of worker turns worth of development is absolutely devastating. It's partly because in the interim, your opponent is losing hammers, food and commerce by the score (a special resource left unworked for even just 20 turns is probably costing 60 factors of production), but that disguises the true effect.
Food is a very marginal product in the game - you're almost always spending the majority on "food upkeep" and so little differences can mean massive relative changes in "food profit". Similarly, once you've developed a bit, commerce becomes increasingly marginal, with all the costs for units, city upkeep and civic upkeep and again, small changes can translate to large percentage differences in commerce profit - and so large changes in science rate. In a civ with decent-sized cities, you're suddenly using pretty much all your working population on food just to keep from starving, thus drastically reducing your ability to generate commerce and hammers - well beyond the loss just from the lost mines and cottages. What little commerce you are now generating goes increasingly towards just paying your upkeep, with a resulting near-total loss of scientific ability and possibly even complete bankruptcy.
Production comes in a dismal third, meaning you have a hard time developing your empire and building the things that would alleviate your problems (i.e. workers and military). It also doesn't help the whole situation of just feeding yourself when you lose a whole load of health and happiness resources, or your commerce when you lose masses of trade income either.
Because of this marginality (is that even a word?), a pillaged opponent is now spending all their efforts just keeping their head above water.
And that's just the pure effect of the pillaging, without considering the consequences when you're also embroiled in a war. Production capacity for building units goes way down, and without resources you can't build your best military units to stop it anyway. Pillaging units draw forces away from the front to deal with them, as well as to garrison cities that they might be near. This division is even harder when you've got no road networks left, and makes pillagers progressively harder to attack. It also makes it much more difficult to get reinforcements to threatened cities, so a pillager with a semi-decent main attack force has improved chances of taking a couple of outlying cities too and crippling them even harder.
And for the attacker? You don't need a great number of troops, and they don't necessarily need to be particularly high quality. You get a whole bunch of money while you're doing it, that can easily offset the cost of having them in enemy territory. You're not fighting many actual battles so you're not losing many units and you're not generating much war weariness. So with very little cost you can keep the "war" going well after you've finished pillaging, to ensure their workers and settlers stay inside and hinder them that much more every turn.
Pillaging rocks, and a well-pillaged enemy is dead - even if they don't know about it and even if the score doesn't reflect it, they're dead.
Oh yeah and it lets you quote all this sort of stuff about "defeating your enemy without ever fighting a battle" and "using an enemy's strength against him" from Sun Tzu or Yoda or whoever which makes you sound totally deep and philosophical.