Shortened clutch and brake levers are slightly harder to pull. Full length levers provide a little more leverage for the user. Just like using a lever to move something heavy, the longer the lever, the easier the job is. Shorter levers look cool, and if your lever is fairly easy to pull, there is no reason not to use them. It is really nothing more than a preference. Short lever and long levers both do the same job. Just know the shorter lever will take a little more effort to pull than a standard-length lever.