1. For More Aerodynamics
To make oneself faster is probably the most frequently assumed benefit of leg shaving. Less leg hair, less drag -- that's the thinking. The problem is that the aerodynamic advantage gained in this area would be so incredibly slight as to be virtually undetectable. This is especially laughable when you think about a guy like USA cyclist Dave Zabriskie shaving his legs to go faster, and then keeping that big honkin' mustache.
But, regardless of what actual testing in a wind tunnel would show, like so many things in life, a cyclist who BELIEVES that having smooth legs is helping is likely to see (or perceive) a positive effect as a result.
2. Easing Healing of Road Rash
One of the reasons for shaving is that it makes the healing of "road rash" -- that painful patch of skin that has been ripped off your body after a nasty fall -- that much easier. Cleaning the wound is simpler with no leg hair in it, and you lessen the chance of infection in addition to minimizing the painful problem of leg hair getting trapped in the scab as the would dries out.
3. Makes Massage More Pleasant
One of the best things about being a pro cyclist is the massage sessions that follow a day's riding. Having clean shaven legs makes it easier and more pleasant for the trainer to perform massage. Plus, there's no pulling on the leg hair when they really start working the muscles hard.
4. More Attractive Appearance
To many people, shaved legs simply look better than hairy ones. Tanned, muscular and lean legs are enhanced by smooth skin. After all, that's the same reason weightlifters shave their body hair -- to look better when they're strutting around stage. And anybody who has followed pro cycling knows there is no shortage of preening in the peloton.
Maybe one of the strongest appeals to shaving one's legs as a cyclist is the tradition involved. For years cyclists have simply shaved their legs, and to shave your legs as well marks you as one of that group, regardless of how fast you actually go on a bike. Half of being a cyclist, some might say, is looking the part.