The desire to shave a millisecond off response time in a gunfight leads people to do some idiotic things.
I was behind a police officer in line at a convenience store a few weeks back. I glanced down at his sidearm, just vaguely curious what kind of hardware he was carrying. It was then that I noticed that he had his gun in his holster with the hammer cocked.
Seriously, the hammer was cocked. In his holster.
I don't know about his particular gun, but with the hammer cocked on my SIG, the trigger pull is down to about 2 pounds. Which basically means a strong exhale will fire it. I would be terrified drawing a cocked gun out of my holster, for fear it would go off during the draw.
And if he cocked it but kept the safety on, is flicking off the safety really that much faster than pulling the extra nine pounds or so on the first trigger pull? In my opinion you're better off not having the safety on, and not having the gun cocked. In fact, on a lot of modern combat pistols (like my SIG) there is no separate safety. No reason for one.
And all of this is in service of gaining a half a second advantage that will only matter if you get in a quickdraw situation, which NO ONE EVER DOES. Cops don't quickdraw with badguys. It happens so rarely that you'd be more likely to save yourself by never going outside without your portable lightning rod.
I'd be willing to bet it's guys like Mr. Ready for the quickdraw contest that blow their ass cheeks off.