When are Dark Eyes the unit you take? When you are fighting lower-armored opponents and you want more than one chance to hit, as they might be higher DEF opponents like Blade Maidents. If you hit a blade maiden with a 12 x 2 damage attack (ie from killing stroke) most likely they will fail the first armor save, thus you wasted that potential second wound. Also you might miss especially if your a unit like Bloodbone Warhammers or another unit without the great CC that some units have, combined with an opponents high DEF and you can miss a lot actually. So you go with less damage, but more chances to hit. Once you get into close range of charging and attacking that is when that 3rd action kicks in and kicks ass. you can potentially plow through a unit of blade maidens. Of course those maidesn can do the same to you too potentially but Dark Eyes work well in such situations, or should and of course flukes do happen. It could be that God personally cursed you to roll like crap that day either that or some random Gypsy fortuneteller who put the evil eye on you and you don't even know it. Who knows, but the Dark Eyes probably aren't to blame.
The unit I have found less use for, but they are useful, are wailers. I suppose if you take them use their wail fearing ability, otherwise what is the point in taking them. I know when I play my Scavenger I love his Howl and always use it cuz its fun.
