Using traditional casting techniques often wastes precious source material. Additive manufacturing - building parts up layer-on-layer from 3D digital data - pro

Using traditional casting techniques often wastes precious source material. Additive manufacturing - building parts up layer-on-layer from 3D digital data - produces almost "zero waste". "To produce one kilo of metal, you use one kilo of metal - not 20 kilos," says Esa's Franco Ongaro. I don't understand. What traditional casting technique makes 95% of your metal unusable?