...but I don't understand why someone would do it when you can CC and be (IMHO) more effective in stopping any potential threat.
We all have opinions and set priorities based on those opinions. We all generally agree that violent crime isn't spontaneous, it occurs in stages:
Stage 1: Intent
Stage 2: Interview
Stage 3: Positioning
Stage 4: Attack
Stage 5: Reaction
Many of us hold that it is better to derail the chain-of-events at Stage 2 or 3 instead of waiting until Stage 4. Waiting until you are already being attacked before doing something seems, to some of us, a backwards way of effecting one's defense.
All of us (I hope) desire to never need to use our carry sidearm. Drawing a gun in self defense is lose-lose almost every time. You may be successful, but you still lose. Even if completely justified and with good witnesses to verify your side of the events (best case), you will not be just getting up and going to work like any other day after having shot someone in self defense. The ride has just begun. Criminal court, civil court, sleepless nights, etc, all are your future for months or years. Were you with your family when you shot that dirtbag? Even with a knife in his dead hand, your kids may not understand the nuances involved, but they will understand that you shot a guy dead, and blood, and flashing lights, and shouting, and handcuffs.....
I don't want to merely be successful in a violent crime, I think it would be better to avoid that entire process.
Note that when you are carrying concealed you appear EXACTLY the same as that unarmed guy walking around in public. We can argue what "might" happen, like a criminal targeting you for your sidearm, however if we examine what has happened historically (called evidence) we find that unarmed people (and the ones that look unarmed) are selected for Stage 2 every single day.
Not all agree! And that's OK. Those of us who carry openly will never (and never do) disparage those that conceal. Most of us do both anyway.