Some of the benefits of driving safely are obvious (you are less likely to die). But some are a little less evident. Have you ever thought about the gas that you save by driving the speed limit? Or the incredible amount of money you will save on your car insurance? These things will save you a ton of money over your lifetime. Being a good driver is much more than just staying out of accidents.
Speed limits have a couple of functions. They limit the speed on a freeway to a safe amount (theoretically), and they are optimized to improve fuel efficiency in cars. Driving the speed limit, which is slower than most people drive, will lower the amount of drag that is put on your car by the air. This allows your car to move freer through the air and get better gas mileage through better aerodynamics. If you couple this with properly inflating your tires to the recommended PSI and not running the air conditioner you are going to squeeze every MPG you can out of your car.
Safe driving can help prevent accidents. Obviously, not all accidents can be prevented, but you are going to reduce the chance that you are the cause of the accident. This is going to keep your insurance premiums dramatically lower. If you have already been in a car accident that you were at fault for you have seen what happens to your monthly payment. Safe driving also lowers the risk that you are doing something dumb and getting a ticket. Tickets will also increase your insurance premiums.
Drive smart, drive safe, and save a ton of money!