It's a common question.
Not too long ago, a guy got jumped in a Dayton, Ohio gas station while pumping gas. By his own admission, if he hadn't had a chambered round, he probably would never have been able to chamber a round once the fight started. It was two on one, him vs. two druggies. He managed to free an arm, draw his firearm and shoot the one in front of him. The other one remembered pressing business elsewhere and departed.
Had the victim not had a round chambered before the attack started, he probably would have ended up severely beaten, his car stolen, and probably shot with his own gun.
I NEVER carry without a chambered round. As the saying goes, no plan survives contact with the enemy. I'm not going to assume that somebody who causes me to need to shoot them is going to facilitate me doing so.