Article on effects of canting on weapon accuracy.
http://www.accurateshooter.com/optics/canting-effect-on-point-of-impact/
http://accurateshooter.net/Blog/cantedhold2x350.gif
Realistic, correct and damped (no infinite lean speed) lateral camera displacement in peek, lean or fire from cover with correct un-canted weapon handling gives the virtual Player improved proprioceptive and virtual kinesthetic cues as to how well covered he is (or isn't) when firing from a position of cover with a cover stance.