I was trained in the school of "if it's got one, use it."
1911 - chambered and safe. Had a kid once look at my hip and warn me that my hammer was back as if it would magically jump out of the holster, disengage its own grip and thumb safeties, and start dropping the hammer without me. My answer was "Yep. And?" He left.
Glocks / XDs / M&Ps / other random battleplastic... chambered and ready to go.
Kahr - chambered and ready to go -- DAO trigger means not having to tell the floor "I'm sorry."
I have watched (in horror) a handgun tumble toward the floor on more than one occasion working as a range officer and have waited for the *BANG* -- thankfully, dropping the vast majority of autos made today simply leaves a dent in the linoleum and a flat spot on the front sight and little else.
I remember being nervous to carry "cocked and locked" -- and quickly got over it. The trick to not being nervous about it is trusting the gun and NOT fiddling with it. Put it on, leave it on, and don't finger$&%# it.
In my opinion, if you're going to carry, you have to mean it. If you're going to mean it, you may not have time to chamber a round before you need it.