To offer a contrary opinion, I’d say not at all necessary on the Deck. You aren’t putting in a pocket with keys or something like you might a phone. You aren’t laying it face down on the screen like you might a phone, because the sticks would get in the way. If you’re throwing it in a bag, you’d be nuts to do without a protective case or cover, and if something is still enough to damage the screen a screen protector isn’t going to save you. If you drop it, it’s going to take more severe damage to things like the sticks, triggers, bumpers, etc. before it ever touches the screen. If it’s a rough enough fall to actually cause screen damage, the screen is the least of your worries. It’s probably dead at that point.