Hot water cleans more effectively than cold water when it is used to wash linens and whites or very dirty, greasy clothes. This is because higher water temperatures work better to effectively remove germs and clean heavily soiled garments.
According to About.com, hot water is harmful to some clothing Darker colors often come out faded, shrunk, splotchy or wrinkled. Delicate fabrics should never be washed in hot water as they do not respond well to high temperatures. Slightly cooler, "warm" water provides cleaning action strong enough for moderately soiled clothes, without the risk of fading and shrinkage. It is ideal for jeans, lighter colors that don't run and sturdy fabrics.