Even the Master Chief has to protect himself from getting battered. And as much "pansey" as it may seem, the tactical advantage for any player would be benaficial. I was playing Halo2 wth my freinds the other day, and when one of my team mates was about to be blown up, right when he was going to take out a wraith, I jumped in front of the missile, spreaing him, but turning my MC into chunks. And I had my self a energy sword too. Which took me ages to obtain. If I had a sheild, the bulk of the blast may not have killed me, and I could have charged towards the attacker.