Zero bloom doesn't work with Reach's movement physics.
Edit: Let me elaborate. Reach's physics, even when set to "classic" style movement, does not allow for proper strafing like in previous titles. It's like when you dodge left and right, you're suddenly swimming in Jell-o and can't maintain full speed.
Therefore making ZB gunplay suck IMO because most of the time if you get the first shot you're guaranteed the kill. ZB sounded good to me but after experiencing it I have the opinion that it simply doesn't fit in Reach.
Reduced bloom pretty much allows for close to mid range spamming to still be effective.
[Edited on 01.23.2012 1:17 PM PST]