Because you only use materials that you need, you can optimize the design of machine parts.
The image above is GE’s lattice cube. The organic design makes it about 1/3 of the weight of a solid cube while maintaining the solid’s compression strength. The part is lighter and still as sturdy as a traditional part.
This example of a high-pressure turbine blade was made from a cobalt-chrome alloy. The blade contains intricate cooling channels that would be otherwise difficult to manufacture. It is a good example of the new freedoms enjoyed by designers using additive manufacturing to make metal parts.