Folks should carry in whatever way makes them comfortable. I prefer to carry with one in the chamber for the following reasons:
The rule of "threes"
Quite a few years ago I attended a seminar regarding concealed carry and the "rule of threes" was discussed. The findings of self defense encounters indicated most happened in three seconds or less, with three rounds or less being fired, and at distances of less than three yards. And, it was usually dark.
I'll mention more in a second, but if I'm confronted I don't want to have to remember whether I have a round chambered or not. I always carry with one in the chamber and I always carry a gun with no external safety to disengage. I always carry in the same location on my body. I don't switch from ankle to shoulder to strong-side etc. It's always strong-side OWB with a cover garment. That's how I ALWAYS practice. In the heat of the moment I want to instinctively know where the gun is, how to get to it quickly and be confident that if I need to pull the trigger it will go bang.
A real life encounter
A few years ago I spoke directly to a young man who had to use his gun for self defense. Long story short, he's at a gas station, confronted by two thugs who try to pull him out of his car as he is trying to leave. They are dragging him out of the driver's seat and he is holding onto the steering wheel with his left hand to stay in the car. Fortunately he has a .45 Glock in the center console - with one in the pipe. After going through the agonizing decision of "is this the time I can legally defend myself?" he decides it's now or never, gets the console open, grabs his gun and fires two rounds into the attacker's midsection. Cops come, he's interviewed, they view the gas station footage, he's released. I think the video may be on youtube if anyone doubts the story.
Anyway, do you think he's happy he chose to carry with one in the chamber? Being dragged out by two men, one hand on the steering wheel to stay in the car, and the other to grab the gun and fire. Not much opportunity to rack the slide... I guess that's how real like works sometimes - no time or opportunity to rack the slide, no iso stance, no "front sight, press". Just get the gun and shoot to stop the threat to your life.
Professional training
I'm not ex-LEO or ninja or ex-SF. I'm just an old legally armed citizen. So to protect myself properly, I've spent considerable time and money on sound training in basic marksmanship and specifically in concealed carry; drawing from concealed, moving and shooting, use of vehicles as cover, shooting from vehicles, handgun retention, contact shots, shooting attackers who try to grab and restrain me, shoot-house scenarios with simunitions, shoot/no shoot scenarios etc. etc.
Not one instructor who trained me, nor any of the high-profile schools like Gunsite, Sig Academy, TDI has ever to my knowledge suggested carrying without a round chambered for personal self defense with a handgun. There may be some, but I submit they are in the minority.
So, again, I respect everyone's decision to carry however they please. For me - one in the pipe, always.