A bushing is a sort of a sleeve, (portion of a hollow tube), that generally would go between the stem (goose neck) and the head set. They provide 2 functions. As a spacer for height adjustments, and to allow a moving joint to be 'snug' while minimizing resistance on the bearings. They can be made of various materials... mostly metal. But carbon fiber is not only strong like metal, but has a superior 'flex' capability (without bending). The bushings under the stem (goose neck) and the carbon fork provide a sort of shock absorption. This helps a lot when encountering a sudden change in road pitch (like when a bike path abruptly goes up), or on a bumpy road.

It's not a 'shock absorber' like on a mountain bike... road bikes are a rough stiff ride. A good intermediate or advance rider will definitely notice, and appreciate the difference. Road biking is gonna hurt. But only in the best way.