Shaving legs isn't essential for riding a bike - obviously.
But we bike racers (I'm a lapsed bike racer) do it.
Why? There are various reasons given:
Theory is that air flows smoother over hairless legs, so even by a miniscule amount, you'll either go faster or save energy. Whether this is actually the case or not, it FEELS faster, and it's often the psychology of it all that makes the difference.
Falling off is a fact of the bike racer's life, and it hurts. Road rash is the most common injury, though worse can happen. The one thing that a rider can't abide is not riding, for any reason. So if there's a way of reducing time off the bike, or mitigating against it, then that will be taken. The theory here is that hairs trap dirt in abrasions which could lead to infection. Remove the hairs, remove potential infection and time off the bike. Also, road rash heals faster (theory) without the presence of hairs, and the skin is easier to clean (true).
It must be wonderful to have a massage after a bike race - I never experienced it, but all the pro's do. I'm told that massaging hairless legs is easier than hairy ones, but maybe Emma can advise on that?
It looks neater, at least to the purists' eye. I'm not racing these days so don't shave my legs, but still think it looks neater.
Are you serious?
Even today I'll eye up a cyclist and see whether those pins are silky smooth or not by way of a simple assessment as to how serious they are, even though I don't shave mine any more. But then I'm not racing, seriously or otherwise. It's a statement - more psychology?
How to do it
Ladies may have views on this. I found the most expedient way was in the bath and use copious quantities of shaving foam. It gets through blades like no one's business and blunt blades hurt! Back of the knees are very tender and a small nick there leads to unbelievably vast quantities of blood leaking out - quite astonishing. So take care there.
Where to stop?
Cycling shorts as you probably know are quite long, so all you need to do is end where the shorts start - but if those health and massage reasons are true then you need to go higher. It's up to you really - but if you also wear speedo style swim shorts then you'll have "hairy cycle shorts" which might look odd.
Drawbacks - girls
They might think it's odd, a bloke with shaved legs, unless they are from the whacky world of cycling, or particularly understanding. Bristly legs are ... bristly.