Looking over the published WTC lists, a lot more lists include defenses than I would have expected. I’m sure that a lot of this has to do with specific metas, but as my own meta includes little to no stealth and lots of armor, I’ve found little use for fire pits or powder kegs, and spike traps can be great for controlling enemy infantry, but I’ve found the restriction of not being able to place defenses within three inches of other terrain to sometimes be very restrictive, since you’re required to place it on your side of the table. Barriers are certainly useful, especially when you can place a wall on elevated terrain for your shooty models to camp out, but the possibility of an enemy using a sapper card or the like to remove the wall means the caster will be avoiding that cover whenever it might suddenly vanish.
This all being said, defenses are seldom taken in my play group.
So I’d like to have a discussion about the strategy behind selecting and placing defenses. Given that the specific defenses are chosen after seeing the opponent’s list, you’re obviously going to be choosing with that in mind, and not (for instance) choosing a fire pit when your opponent has no stealth. But beyond that, what’s the strategy behind selecting and placing defenses, how best can they be used, and in what situations are they really good?