When I draw my full-size 1911 (or my S&W69 .44mag revolver) from its homemade under-the-shirt vertical shoulder holster, I can't clear my armpit if I keep the gun approximately vertical during the whole draw ... I HAVE to start rotating the muzzle up during the draw, in order to clear the holster, and start the grip of the gun moving toward the opening in my shirt (that I've created by unsnapping a couple of snaps as my hand slides into my shirt at about sternum-level). So, I HAVE to ensure that BOTH of my safeties on my 1911 are engaged (both thumb and grip safety). I've developed a procedure (and I practice it often) that makes me confident that I ALWAYS keep those safeties engaged until I'm coming onto target. I wouldn't be willing to carry that way with any other semi-auto, even a Sig SAO with a thumb safety ... I want and need that redundancy in safeties in order to have complete peace of mind. The only exception would be a DA/SA semi-auto, carried with hammer down. Likewise, I'm confident of being safe with my Model 69 revolver carried hammer-down (of course!).
In addition, I also had to come up with a drawing procedure that would allow me to draw my gun when I get to the firing line of my range, in order to not violate their rules about sweeping during the draw. The procedure I use is a bit counter-intuitive: I turn and face AWAY from the bullet-stop, so that as I bring the gun out of the holster and rotate the muzzle up toward horizontal, it's always pointing downrange. I then, without moving the gun, rotate my body so I'm facing downrange. I use the same process (in reverse) when reholstering ... the gun never sweeps me or anyone else. Of course, that procedure won't work when drawing in a self-defense situation (there, I HAVE to rely on my procedures for ensuring that the safeties are both engaged), but it also does come in handy whenever I draw my gun at home for non-emergency reasons.