The areas of application for 3D printing grow as more materials and techniques are developed. Be it larger print envelopes, greater accuracy, multi-color and multi-material printing, each new material, technique, performance increase, and quality improvement allows a new problem to be addressed with 3D printing.
Creating lighter weight designs has been an issue since the first engineer designed "Wheel 1.0". Two technologies combine today to take the possibilities of light weight designs further than we have seen before. Combining innovative design algorithms with 3D printing in general and metal 3D printing in particular, allows designers to create extraordinarily light-but-strong designs which can now be produced. (See: What's behind generative design)
The image here shows four variations on design which maintain the design requirements for strength and produce progressively lighter results. In this case, the algorithm designs are not only impossible to design using traditional methods, they are equally impossible to manufacture without 3D metal laser-sintering printing techniques.