By warming up your muscles (I am assuming you mean by stretching and doing jumping jacks and such, not sitting yourself in front of a heater...) you will have a better overall workout. Your muscles will be ready to work and you will not tire as fast. Also, your muscles will feel better the next day because you got them ready to work out.
One result of warming up your body muscles before exercising is that it will increase your body temperature. This will reduce the chance of getting muscle injuries.
