Light and Fast comes from fell running and adventure racing where every gramme counts. In these sports a fairly constant level of exertion means that garment changes are often unnecessary... and you don't expect to be comfortable!
In mountaineering and hill walking light and fast still holds true, but the 'faff factor' comes into play. Changing layers to stay comfortable and dry can slow up progress significantly, especially if different members of your team are changing at different times. It's complicated further when you're festooned with sack, slings, body coils and harness.
The vents on FurTech garments mean that they can often be worn all day come 'hail, rain or shine', significantly reducing the 'faff factor' and increasing speed across the ground.
Of course, light doesn't just mean light. It infers weight in comparison to warmth, durability and functionality. Does that ultralightweight shell have a helmet compatible hood? Does it have insulation? Can you vent? Will it seal out spin drift? Will the sleeves go over your gloves? Try comparing FurTech weights with a shell jacket and hooded fleece with pit zips.
FurTech garments are significantly lighter than other types of layering system because they don't have membranes, taped seams and extra zips and trim. And they come with a whole host of other benefits... the Sight'n'Sound Hood for instance.
FurTech also offers a better warmth to weight ratio than our closest competitor due to a thicker fur lining. However, the Rain Vents allow more comfortable summer use! If it's not raining and you are warm enough you don't need to wear it.
That said, I wouldn't go fell running in a current FurTech jacket (we may be introducing something for Adventure Racers in the future).