popejubal
Emperor
This is really a question for all levels: WHat's the use in attacking an enemy stack with Siege in your territory?
If you attack with Siege, the enemy will gain promotions, sit down to heal, and then rape you anyways. And it lets them open up a second front against you by making their attacks roughly simultaneous, not staggered.
I also recently discovered that you get more XP when you're in your own territory - even if you haven't built the Great Wall!
I'm going to use both halves of that information to my advantage. I like attacking an opponent enough to give them a Great General (as long as I get enough of a return on my investment to make the assault worthwhile overall) since the AI generally settles the GG in a good production city. I like getting a Great General without bumping up my points required for the next. I like getting my own Great Generals too.

Also, you get to heal quite a bit faster when you're in your own territory, so you can attack with the siege, run the units back to a city (if they survived) and then attack again with the same siege units just a couple turns later. Just a few siege units sacrificed will make the rest of the stack a piece of cake to run down with about 0 further casualties on your own side. Building the Siege units under Theocracy or Vassalage is a big help since 5 XP gets two promotions and you're not going to get more than 1XP per battle no matter what the odds are.
Last thought on Siege units. Catapults are better than Trebuchets for attacking in the field. Trebuchets are better than Catapults for attacking cities. Cannons are better than either - especially since Cannons ignore City Walls/Castles. Anybody know if Castles/City Walls make Cannons and Artillery bombardment rates slower, though?