Those of us who shoot smoothbore guns know how quickly fouling can build up inside the bore. If we neglect to wipe it out after a few shots, the gun becomes very difficult to load.
A few years ago, I was shooting in a muzzleloading shotgun clays competition. While I was running wet patches down my barrels after each shot, I noticed others were not. Instead they were spraying a bit of Moose Milk down the bore after they loaded their powder, wads, and shot charge. During a break in the shooting I asked about that.