It only makes fractional differences in speed of dry. The modern high speed models don't need to rely on a heater element to evaporate the water, the speed of the air flow does the job a lot more efficiently. The heat is primarily a psychological / comfort feature. One of the main reasons hand dryers don't include a heater element or they have the ability to switch it off is without the heater on they are so much more energy efficient. This means better for the environment but also cheaper to run. The heat generated from the motor usually does enough to heat the airflow to a comfortable level anyway and as already said the pros of not having one certainly out way the cons of a seconds quicker dry time.
