Fear is a good ability in one off games, but in Champagnes it's not as good as more characters gain immunity to fear, and higher leaderships.
So in one off games the fear immunity makes Dark Souls better then they are in Champagnes. Most of the Possessed Warbands I have seen Get as many Beastmen as they can, then Brethren then as last resort Dark Souls.
I think that fear is an over priced skill/ability and in Champagnes it really shows.
Realistically Fear has 2 functions,
1. If you fail your leadership test, you cannot charge a model with fear. Meaning that the model basically loses their action for the turn, and it is pretty likely that they will charge you on their turn.
2. If you are charged and you fail your leadership test you can only hit on a 6. If you already have a low enough Weapon skill you might already be needing a 5+ to hit so itís not that much of a loss, also most things with fear are undead, so if they donít kill you on the charge, and you donít kill them on the attack back then more likely then not you will have a higher Initiative and you will strike first as normal for the next round. So it can screw-up attacks or bonuses that only work on the first round of combat like flails, but for most models it wonít matter as much.