Shaving hair other than on the face has been practiced for thousands of years, in cultures across the world. The main motivations have been for cleanliness and hygiene, and for appearance. The latter has indeed been the motivation for about 50% of the population of North America to shave their legs.
Athletes in particular have a separate stimulus which causes many of them to shave body hair: performance. Hair adds substantially to the surface drag of a rider or swimmer, slowing the rider by very measurable seconds. Skinsuits of lycra or spandex are also used to reduce friction over conventional textiles and to cover arm hair, but the legs are left bare during season races.
Shaved legs are very nice for the rubdowns following a workout, which clear out the lactic acid and other toxins to speed recovery. However, simply doing twenty minutes of gentle spinning has been shown to reduce stiffness and soreness, and to increase performance the next day, even more effectively than rubdowns.
Hair certainly reduces cleanliness, but poses no real risk in an accident. It is not true that General Schwarzkopf had all the troops shave their legs and arms before going into combat to prevent infectious hair from killing injured soldiers, and I am sure it will never happen. There is no medical proof that hair presents any hazard when crashing on a road with dirt that gets into a wound. It must all be thoroughly cleaned anyway if it goes beyond superficial road rash.
Some people use preparation for crashing as an excuse to shave, but you don't really need an excuse other than vanity. Just as body builders, swimmers, and women display their legs, if you feel like shaving, then go right ahead.