You mean with a round in chamber? Yes! I would have serious doubts about the qualifications of any "pistol instructor" who says not to. If you are proficient with your firearm it is perfectly safe to have a round chambered. If you're not confident that you are proficient , then don't carry at all. When you see cops in movies chambering a round before they engage a bad guy, that is Hollywood bunk. They are always loaded to capacity with a round chambered.