The idea behind them is it reduces barrel movement in the time before the bullet clears the barrel. Take a 1911 with a 4 lb trigger. You steadily apply pressure until it reaches 4 lbs, the sear releases, and then the trigger weight drops below 1 lb meaning now the trigger goes rearward abruptly gaining momentum the further it travels until it hits the stop. During all of that movement kinetic energy increases until it hits the stop and jars the gun. By reducing the amount of post release movement, you reduce the amount of disturbance to the pistol. This is why target pistols have trigger stops.