Warming up is pretty important when considering muscle, joint and tendon longevity. It also helps to increase your energy level prior to exercise, which in turn helps you get the most out of your workout.
A good analogy for warming up, is the rubber band. Once the band has been stretched several times it will begin to stretch further and quicker from then on. This is very much what our bodies feel like when we stretch before exercise. Once we are warm, movement will feel easier and more fluid.
Essentially we are trying to avoid injury. We do this by increasing the body’s core and muscle temperature through movement - gradually bringing it to where it needs to be. When we are warm the body speeds up. More energy is produced once the muscles are warm, which increases reflexes and reduces the time it takes a muscle to contract. At the end of a warm up you should have greater range of motion (be more flexible) and be mentally ready to attack the workout.