drilling holes makes the shoes lighter...when used in conjunction with heavy springs results in delayed clutch engagement which improves of the line punch....because it takes longer for the shoes to engage, the engine is "starting" to engage the clutch bell when the rpm's are higher.
The trick to aluminum shoes involves a few things.
1.) your driving style....if you are constantly feathering the throttle, youre inducing "slip".... slip = heat = wear
2.) what engine youre using....
3.) maintanance....clean and deburr your shoes after every race day or bash session.
4.) a relatively "clean" shoe contact patch....makes a big difference. If the surface is gouged or pitted or laced with melted aluminum, get a new bell.