How do body kits help your car?

Most body kits are said to help your vehicle go thru the air better and routes the air either under, or around and past your car so you can go faster, or get better gas mileage. But you need to fidn out what a body kit weighs. Sometimes you end up bolting on more weight and lose the benefit of the kit as far as any horsepower or gas mileage gains. Some kits are made to allow you to put wider tires on your car. Some kits are made to direct air to a cooler or turbo Some kits are made to hold your car down in the rear at high speeds Some kits are made to press your car down as the air flows over it improving adhesion to the road Some kist are just made to make your car look different Some kits are made to make your car look great Some kits are made to make your car look stupid But it's your car............