The insert levers refine control function. For over 15 years we have been making special ratios for the top riders and now you can have the same adjustment options as the factory guys. The brake levers can go from feeling like there is air in the system with a 14mm insert to “something is wrong, the lever is hardly moving” with a 19mm insert. The clutch levers compensate for Rekluse style clutches. The slipping type clutches seem to need a pinch more “pull” at the lever to get full disengagement. Hydraulic clutches benefit greatly from the ability to overdrive the master cylinder and get that “pinch” more pull needed.