"War by the rules"

I have a question: what does it mean when "fast battle" is enabled? Do you only fight using fast battles? And does it also apply to battles between heroes? o_0

When attacking any neutral army, a "fast battle" result is displayed. If you are not satisfied with the losses, you can click "fight manually."
Of course, it's usually better to fight manually, but sometimes when the battle is not very important, it saves a lot of time... the only downside is that the computer always uses a lot of mana.
And, of course, if a battle takes place between two players, the manual battle mode is immediately activated (no "auto-battles").