Fairly common for competition guns. Mostly for stuff ike Steel Challenge or Bianaci.
One of the major goals with a competition guns is for it to stay flat. Meaning that the gun recoils in a different manner. Instead of the muzzle tilting up and thus the front sight moves off target, you want the gun to come strait back toward you. That way you have the fastest possible follow up shot. If the gun does stay flat like he claims, then that's pretty good.
The lightened slide also cycles faster. There are two schools of thought. Some people like to add weight (that doesn't move)to the gun. That means heavy everywhere but slide and trigger. This helps absorb felt recoil. Other like a all around light gun. They feil they handle recoil when rapid firing just fine, but want a gun that swings and indexes faster between targets. For stuff like Steel Challenge and Bianaci where there is no power factor, people are using light loads, so recoil is at a minumum. Thus the light, and fast indexing guns have a advantage.