We used to drill components of our motorbikes back in the 70s (side covers, levers, etc.). I don't think we saved any real weight compared to just taking a dump, filling the tank partly full, wearing less leather, etc, but it individualized our bikes. I certainly wasn't serious earlier, but I see now that people are still practising the age old art. I don't think I'd mess with rims in a bmx or downhill environment.