I've had my back seat out for the last months... Easier to haul stuff around..
FWIW, the seating area weighs about 5lbs, and the fold-down seat backs are maybe 20lbs each... Minimal weight reduction for such a loss in looks, cabin noise insulation, etc..
..unless you're trying to shave that last 1/10th to get your quarter mile times into the 12's I wouldn't do it.. Not for weight..