The setting was designed to keep a bullet roughly inside the vertical height of the average human torso out to 300 yards. IE with the battle sight setting, (these are the M1873 numbers, but you will get the idea) at 50 yards the bullet strikes 13" high, 21" high at 100 yards, 16" high at 200 yards, and 17" low at 300 yards. With the rifle held parallel to the ground, there should be no safe space for a man inside the critical 300. We still do this, only today we call it "optimum point blank range"
Remember, the critical distance in battle since the inception of firearms has always been 300 paces/yards/meters. With the invention of Smokeless, military thinkers the world over doubled that to 600 yards, only to find out even today, that the critical engagement distance still remains 300.