Looking at the guide, it says the following about Fanaticism:
Fanaticism (Orcs)
Fanaticism focuses your army on combat and war, increasing their offensive efficiency for several days. Unfortunately, a side effect of this desire for blood is that they will not be as capable of capturing land and resources, and your armies remaining at home -- bored and frustrated for not being at war -- will fight less effectively on defense.
Effect: Increases your offensive military effienciency by 5%.
Effect: Decreases your defensive military effienciency by 3%.
So in the spell description it says you have lower gains, but in the effects this is not listed. Can anyone confirm whether the combat gains are reduced by this spell?