I carry a tiny .380, an MPA Protector, because my body, my preferred style of dress, and the nature of my job make it impossible to adequately conceal anything larger.
I'd prefer to carry the Taurus 709 Slim (9mm), but I just can't hide it well enough when I'm bent over a table to mark something at the end of a yardstick, leaning forward to work on a sewing machine, or stretching to reach things over my head.
While I know that this is not the gun for military or police purposes and that it would be utterly unsuited for a prolonged combat I also know that:
A. Its a better weapon than my thread snips or my steel yardstick.
B. Most defensive gun uses are resolved simply by presenting the gun with an attitude of willingness to fire it rather than by actually shooting.
C. No one who decries the inadequacies of small calibers is going to volunteer to take 6 shots of .380 to his center mass.
Life is full of compromises. If you can conceal a larger caliber gun effectively and shoot it well without drastically altering your life then its probably a good thing to do so. But if you can't do that then carrying a smaller gun in a smaller caliber is better than the thread snips.