Drilling holes into cymbals alters how they sound. It typically cuts out some of the resonance and gives the cymbals a trashier tone. This is why you’ll often see cymbals with holes in them being called “trash crashes”. Cymbals with holes in them often make fantastic additions to cymbal stacks. As having a trashy sound is a desirable trait in a stack, the cymbal with holes will be the biggest contributor to achieving that sound.