Just as a demonstration of Devin's superior singing abilities. If you have the time, watch the whole thing. You'll also notice that he's a top notch guitarist, to boot. Boot is pun because he's Canadian.
No Tom Araya fans? Maybe not the best of all time, but I don't know a metal screamer whose voice better suits his band's music than Tom. Plus he gets extra points for looking like a frightening degenerate on stage. "South of Heaven": LINK