Charles did a post not to long ago(or was it 1 or 2 years with articles of a man who got into a deadly force situation and he was shot dead because he did not have a round chambered, and that precious second or 2 to draw, rack the slide and get on target cost him his life.
I wish I could find that thread. I looked but couldn't find it.
Edit to add: With my SA semiautomatic pistols, I ALWAYS carry a round in the chamber, as most of you do, and when carrying my DA/SA always a round in the chamber in DA mode. Always. And I'm with Liberty. I prefer DA/SA to SAO.