The Metabolic Diet is similar to this type of plan, and Dr. diPasquale actually says to keep your fat intake "moderate" on the weekends and lower your protein more instead.
The basic reasoning is (and the basis for any low-carb diet) is that your body actually adapts to using fat as fuel. And as long as you continue to feed it fat, it will continue to use it. For 1-2 days, eating lots of carbs will be less likely to make your body switch back to a carb-burning metabolism, if you keep feeding it a moderate amount of fat.
By going low-fat and high carb at the same time, your body will have no choice but to make the metabolic switch back to a carb-burning metabolism. This in turn will make your suffering during the week much less effective, because you'll have to spend a good deal of time just reversing back to the fat-burning metabolism, instead of burning fat all week.