The thing is, on large maps during long games, when your army is already decent and the player character is rushing to attack the enemy's city and its hero, you can easily skip minor neutral units on the way using a quick battle to save time, as they would be defeated without losses anyway. But all other battles are best fought manually, and it's also more interesting (this is practically the whole point of the game).
I used to do this sometimes (and still do occasionally) – before a good battle, I save the game, then I do a quick battle first – I look at the results, what's left, who won, and then I load the save and fight the battle fully myself, or vice versa. The results are sometimes really strange:
The same battle, the same conditions, but the results are very different – sometimes a quick battle is won almost without losses, while in a normal battle almost all troops are lost; sometimes the quick battle loses where it's impossible to lose. But overall, I've noticed that in a quick battle, with a normal setup, the losses are much higher than in a normal battle. And in general, it's a bit silly to use AI against AI, and that's why the AI "goes wild," and all sorts of bugs and glitches appear...