As always happens when someone asked about carrying a revolver, the conversation takes a left turn to "capacity". Rightfully so I suppose as limited storage capacity seems to be the big drawback of a revolver. So lets talk about "capacity". Why would anyone carry a 45ACP or even a 40S&W instead of 9mm in the same size platform, and give up 15-20% capacity? The reason is there are things that people value more than capacity. The 45ACP and 40S&W people value bullet size more than they value capacity.
I value a 5 shot revolver over the capacity of a similar sized semi auto (7-8 shot) because a revolver doesn't depend on a magazine, the ammo, my grip, interference of the slide, etc. for continued operation.
The capacity of a semi auto drops to ONE if the magazine is unfortunately ejected in the frenzy of fighting for your life. The capacity of a semi-auto drops to ONE if the slide doesn't completely cycle for any number of reasons, the capacity drops to ONE if you limp wrist it because you just got punched in the temple. The capacity drops to ZERO if you pull the trigger on a bad primer.
If you have a revolver and any of those things happen you just keep pulling the trigger and it'll go to the next round.
I you stop thinking of "capacity" as how many rounds are "stored" in the magazine and start thinking about capacity as how many rounds can be brought into action with just a trigger pull, there are a number of defensive situations where the revolver actually has a huge capacity advantage over a semi-auto. The capacity to continue firing multiple rounds with little regard for outside influences on the firearm.