Originally Posted by Rpg
If I went to a crime scene or to participate in an arrest in an official LEO capacity, I'd carry an extra magazine : an additional 7 or 8 rounds.
Never in a civilian capacity.
There is one reason I disagree with that. I haven't carry a semi-auto for a long time, but when I did, I always carried a spare magazine. Not because I was worried about running out of ammo, but because the pistol has a weak point which the revolver does not share: you can accidentally lose your entire load by pushing the mag release unintentionally. Hypothetical? No.
In the video below, an Oregon State Police trooper's life was probably saved because the perp accidentally dumped his mag after the first few shots; you can see him come back and pick it up. The trooper was wounded, the perp found dead by the side of the freeway a few miles away.
If it can happen to a bad guy with military training, it can happen to you. Not a problem with a revolver.