Its largely an aesthetic thing, more for the looks than for the actual weight loss. Some did try and use drillium to shave off a few grams, but that was more for the morale boost/mental aspect, than for achieving some goal in the bike's weight. This is why you often see milling, paint accents and pantographed logos accompanying drillium.
Someone correctly and artistically doing drillium is an art in itself. They use custom jigs and templates to achieve the patterns and maintain straight lines, or smooth radii in curved uses. Two of the regulars here, Otis and Drillium Dude have become very well versed in properly and professionally doing good looking, artist level work on components
.
A few examples of Drillium Dude's work:
BikePorn.org
I wouldn't even dream of attempting
to drill, mill, or even paint details on a component, not a great idea
when you have tremors in your hands from PD
.
Bill