I haven't read much on this particular plan, but it sounds like "carb cycling", and carb cycling certainly does work and isn't dumb. Carb cycling has been used for years by body builders to target "fat" loss over weight loss. The very basic idea is that when you restrict your carb intake (and burn thru your glycogen stores w/depletion style work-outs (P90x, Insanity, etc), the hormonal response is for your body to turn to its fat stores for energy. But it's only temporary because of adaptations (Leptin and Insulin go down, ghrelin and cortisol go up, etc ) and if you do it too long you'll switch to breaking down protein (muscle) for energy. You'll continue to loose weight, but not specifically fat. That's what happens to people who have been on Adkins type diets for too long. They get smaller, but their weight loss is from fat and muscle. they become skinny-fat with no tone or definition. So to correct this, what you do is a periodic re-feed of carbs (i assume that's what carb nite is). what this does is it resets your hormonal responses from the "starving" phase back to a "fed" state. and combine this w/a power/HST type workout (typical heavy weight/low rep) and you can actually be anabolic for a few days. You have to be genetically gifted to add muscle and lose fat at the same time (or be juicing), but you can at least provide enough stimulus to preserve the muscle you have while targeting only the fat.
but yeah, fiber is necessary. ;-)