The golf setup is the first step to having a better golf swing. It's important to have an athletic position and also have good balance. There are 3 basic angles you want to see from the down the line view. The first angle comes from the knee flex. The second angle is from the bend at the hips. The third angle is between the arms and the club shaft.
With your back you want to have your spine straight but tilt forward on an angle so the upper body is slightly over the golf ball. Your belt buckle should point down towards the ball. The arms should hang down naturally without locking the elbows. You want your weight to be towards the middle of the feet and you should feel that you are balanced and ready to make an athletic motion.
It's important to bend enough and have good angles because this will help you stay in your posture better as you make your swing. A common swing fault is to stand up or come out of your posture too early before you hit the ball. Bending down more makes it easier to maintain these angles as you are swinging and turning.
If a golfer was going to error on one side either being bent too much or not enough, it would be better to have too much bend. It's helpful to get exactly the right amount of bend in the setup but you can sometimes get away with being a little lower.
If you maintain your angles correctly from the setup as you make your swing, you'll get a lot more power and naturally be able to swing on a better path and swing plane. Maintaining these angles as you swing and especially at impact will help you create leverage and generate more power which will lead to more solid contact and compression of the golf ball.