I think unless you are eating straight sticks of butter, there is nutritional value to the foods you are eating that have fats in them. I also think that the fats maybe act as a bit of a lubricant (ex. if there are not carbs to hold onto, then the fats are less likely to have anything to stick to)? That is probably wrong, but in my own head, it is the only way i can rationalize something that doesn't quite make sense.
You don't want to get into the habit of eating too few calories. Your body will go into starvation mode, and will hold onto every extra pound. If you cut out your carbohydrates, and then want to cut down on your fats, I honestly don't know where you would get the bulk of your caloric intake from. I have a hard time reaching over 1300 right now, and i eat ample amounts of fats...