It's not so much "needed" as it is a physical consequence.
The empty weight is the weight of the aircraft itself - without fuel, crew, passengers, cargo or weapons.
The absolute empty weight of an aircraft, cargo container etc.
Gross weight (Empty weight) of the F-14 is 43,735 lb.
The Gross Weight (Empty weight) of an X-15 is 14,600 lb.
Unusable fuel and undrainable oil.
The weight of an aircraft counteracts the lift produced by an aircraft. The heavier an aircraft weighs the greater the lift needed to get off the ground.
The aircraft, un-useable fuel. No pax,pilots or baggage
The A380-800's empty weight is 276,800 kg (610,000 lb), and the A380-800Freighter's empty weight is 252,200 kg (556,000 lb).
If the cg is not with in range the airplane will crash.
That depends on the weight and design of the aircraft.
DOW (Dry Operating Weight) in aviation refers to the weight of an aircraft when it is empty and without any fuel or payload. It includes the weight of the structure, systems, equipment, and furnishings of the aircraft. DOW is used to calculate the aircraft's performance, fuel calculations, and maximum payload capacity.
Lift, Drag, Thrust, and Weight. (Not counting Money)
There are three "common" weights used in commercial aviation. The first is Empty Weight which is the weight of the aircraft as it comes from the manufacturer. To this weight, the operator adds the weight of its normal equipment such as galley equipment, safety equipment, fluids (oil, hydraulic fluid, unusable fuel, water, etc.), and normal crew to come up with a Basic Operating Weight. The BOW is often averaged for the fleet and that figure is what is used in calculating the Take Off Weight for each flight. The TOW is the BOW plus fuel, passengers, cargo, and any extra equipment needed on that particular flight.