This is an interesting question, as even at full dark green everywhere, you can still be wounded. I frequently (used to, not so much in newer versions as I believe it has been nerfed) would wear far more armor than necesarry, and the benefit I noticed was that the amount it would be degraded from absorbing damage was spread across multiple pieces, thus lengthening the lifespan of each individual piece. Not sure if it gave an ARMOR benefit, but it definitely helped preserve expensive/rare/both metal armors.