Lol, the shield is not necessary, but it DOES prevent one damage from each creature/weapon source, and it can't be stole, and it reflects spells like Lances and Siphon Life. You could easily take it out and replace it with another Tower, but it's really not necessary. It's a preference thing, I would think. The deck would obviously run faster with that extra Tower, which I guess is the point, but I try to keep my decks based on the theme of the Element. =D