Building a deep section rim in aluminium would result in a very heavy wheel. Carbon is simply much lighter and is the reason it's the material of choice for aero wheels. The lightest carbon fibre wheels have tubular rims, and can be exceptionally light: Lightweight does a set that are 940g for the pair! If you’re a climber and want your bike to be as light as possible, carbon fibre tubulars are the way to go, provided you’re happy to glue your tyres to the rims. The stiffness to weight ratio is also better than aluminium wheels.
Ride quality and performance.
Good carbon fibre wheels can transform the ride of a bike. Stiffness is greater than an aluminium wheelset so for powerful riders, sprinting and out-of-the-saddle climbing, this attribute can make a clear difference to how the bike feels, with a more responsive nature. Some carbon fibre wheels also provide a smoother ride over rough road surfaces as well.
They look cool.
Don't underestimate how important this is. You’ve got to admit, there’s just something undeniably appealing about the way a sleek road bike looks when rolling on a pair of deep section carbon wheels. While many might not admit it, many invest in carbon wheels mainly because of the appearance.