Couple of comments- I don't know about the use of a target hammer, but if you're using a service type holster, most of them require a hammer spur to retain the weapon (particularly in ye days of olde). The second comment is that a hammer spur comes in very handy in the case of a high primer or other minor interference that might prevent a DA stroke from turning the cylinder. A hearty yank on the hammer spur can rotate the cylinder and allow the shot a heck of a lot faster than a NY reload.

Back in the day, I needed to do that during a qualification after a cratered primer hung the cylinder up. We figured that out after the stage was over-there weren't any alibis in our qualifications.