You will obviously have less energy. I have experimented the effects of eating and not eating before exercise. I concluded that when I have something to eat before exercise (not necessarily right before exercise) I am able to run for a longer period than when I do not consume anything.
If you don't cool down or stretch after exercise, there is a larger chance of getting injured then there would be if you do. Cooling down will help remove lactic acid which can cause cramps and stiffness in the muscles.