On a standard rotor, wear can result in a build-up of ferrous material, which is deposited on the brake pad's friction material. The holes on Brembo Xtra rotors, on the other hand, have a scraping effect, which cleans the surface of the brake pad, freeing it form materials that can dampen the brake's response.
There is such a thing as love at first sight, and it often takes the shape of a Brembo Xtra drilled rotor.