Some people want more weight than a SDC, and less than the full length. I've seen holes, panels, internal lightening, and the recent surge in popularity of the Butler cut which all produce a frame weight in between the two ends of the spectrum.Just like tungsten sleeves, hybrid barrels, bull barrels, fluted bull barrels, bushing barrels, or aluminum, steel, and tungsten guide rods, frame profile is a variable you can play with to achieve the balance you prefer.
That said, I'd imagine those holes don't take out a ton of weight. Maybe someone with an FGW gun can comment?
Yes it's sarcasm those are just for the look nothing more, like most lighting cuts they just look cool