In the hands of a pro, the Turret Gun is devastating. If you're going to wield this piece of heavy weaponry, you'll want to rip it off its mount and move around with it. The camera will shift to a 3rd person view, and like the Missile Pod, you'll be slowed up considerably. Like the man says, you got to know when to hold 'em and know when to fold 'em. Check the video for a perfect example of knowing when to drop the Turret Gun. You'll have to decide on a case-by-case basis when to trade firepower for mobility.
