Adequate* "stopping power"** in a small, lightweight, ease-to-conceal in virtually any attire package.
Basically, you get the power of snubnose revolver loaded with standard pressure 158gr .38 Special in a package that is thinner, smaller, lighter, and with more ammo capacity.
That's a bit of an oversimplification, but that's the gist of it.
*I say that it's adequate, because for anything but fantasy combat in which one can overcome the massive disadvantage of fighting multiple armed assailants in the street all by their lonesome by simply bringing more gun, it is indeed adequate, but then again, James Bond handled similar fantasy combat situations with a .32 PPK, so...
**I use the term "stopping power" for lack of a better term, please refrain from writing an essay on how there's no such thing.