Excuse me Sam, but it seems to me I have been told numerous times by various advisers to avoid canting the sights, which in case you are unaware, means tilting the gun to the side as this is improper sighting. I quote the late Col. Cooper because I felt he summed up the situation best. I have never before this thread known of any SERIOUS students of marksmanship deliberately holding the pistol improperly and I maintain that they did in fact learn this from the ghetto gangsters who seem quite fond of this improper technique.
No worries, SP! I understand where you're coming from! Before I started various kinds of competition shooting, I'd never heard of it either. But, really, the more I think about it, it isn't just sound technique for action pistol (and bulls-eye, apparantly!).
A couple decades ago when I started shooting 3-position small-bore, I was taught to cant the 'ol Anschutz slightly to maintain the correct body posture. I was reminded of that when I saw a high-power rifle techniques video put out by one of the AMU guys a couple of weeks ago. In off-hand, he got his stance perfect, brought his M-16/AR-15 up into position, and then rolled (canted) it hard over against his cheek. (Bring the sights to your eyes, not the other way 'round.) And that was a STRONG 15-20 deg. cant, too, not just slightly out of plumb.
The idea of using it for one-hand pistol techniques is slightly different, though the same principles apply. (And SM, Grizz, Diamondback, and others have presented all of that pretty clearly.) How it is applied in IDPA/USPSA might be a little bit different than in bulls-eye -- I thought it WASN'T used in bullseye for the same reasons you've stated! Whoops! -- but the principles appear to be the same.
Remember how pistol marksmen used to stand perfectly erect, strong hand at max extension, weak hand behind their backs or on their hip, etc? Same kind of thing. That used to be the "right" way to do it, and finding a natural point of aim (or adjusting your stance for better balance, canting the gun, etc.) would have been denounced as improper. It took men like Col. Cooper, Askins, Fairbairn, Applegate, and their pals to break a lot of those molds. And the principle of breaking down the hang-ups of the old ways and distilling out only that which works is alive and well, thanks to them!
You really learn something new here just about every day, don't you?
-Sam