A shoulder holster makes it possible to keep a large gun covered when wearing a relatively short jacket, where it would be hanging down beneath the jacket in a belt holster. Also, if you wear a jacket or coat that has buttons you can leave the button that is right in front of the grip of the gun unfastened. But you have to be careful of the "lopsided" look where the side of your chest with the gun looks wider than the other side, which is an easy giveaway. If you use a double harness and carry 2 similar guns, one on each side of your chest it'll look kinda awkward, but won't give away the guns. Another thing to watch for is, with a horizontal shoulder holster it is easy for a perp to reach in and grab your gun if you let him get too close.