I'd rather pop a black capo on than play all the wrong chords.
With metal bands tho, it's usually power chords & riffs. Why would you need a capo to play E5, G5 & Bb5 (all my fave Nuclear Assault songs use those 3 chords).
Anyhoo, I wasn't saying his guitarists should use capos. I was suggesting he try one as a visual aide if the song is transposed up a semi or 2.
The bassist from Kings of Leon has used a capo live (ok, so they're pop rock). Why he did, I do not know. Maybe for the same reason?