Wouldn't you be at a disadvantage if people/bad guy/etc knew preemptively that you are carrying?
That would depend.
If you are in a bank that is being robbed by an organized group of well-disciplined professionals, you would probably be a target.
If you are somewhere and a regular street criminal wants to victimize someone, I'm going to guess that he'll wait for you to walk on by, and victimize someone who isn't carrying a gun. Note that your carrying a gun says something about you beyond the simple fact that you are carrying a gun, and what it says is not what a street criminal wants from his victims.
There have been an unusual number of bank robberies and attempts, lately, around here. NONE of them are perpetrated by organized groups of well-disciplined professionals.
I'm going to wildly guess that, for an average
civilian, most of the time, OC will scare off more criminals than it will attract.
These strategic considerations are likely to change if you are a cop, if you believe that you might be personally targeted, or if you are in places and situations that are likely to be targeted by
professional criminals. I wouldn't OC at, say, the Jewel Mart in Los Angeles, if I had a booth there. I'd CC for sure, though. Same would go for criminal attorneys, and others who might have to worry about professional robbers, crimes of revenge, etc.
Why do I OC (when I do)?
1. I want guns in the hands of law-abiding people to be a
familiar sight, not something that the anti's can demonize easily. OC helps promote that. If nobody sees any guns around, it's easy for the Brady Bunch to build associations of guns with crime, instead of lawful self-defense.
2. It's my
right, and I'm not hurting anybody by doing it.
3. Some guns are easier to carry openly, and if I'm on the way to someplace in the great outdoors, I often put on a holster when I leave the house, not later. So, if I stop for gas or something, I'm incidentally OC'ing. See #2. I'm not going to shove the gun under the seat and leave it unattended, either.
4. It's kinda fun in some circumstances. The other day, a bunch of us went out to eat at a restaurant that is known to have no problem with OC. We all had guns on.
5. I'd like to get some engraving done to a revolver or two. It'd be a shame to keep a piece of art hidden ALL the time.