When I first starting following 3D printing the buzz was about being able to rapidly prototype components at a fraction of the traditional cost of manufacturing a one off item or being able to print complex shapes that traditional manufacturing couldn't produce cost-effectively.
The revelation from this video I watched recently was that you could print moving parts in situ.
But that's just a spanner or wrench. In this latest video they print the entire plane in a single operation. If you can do that you can print a car or a refrigerator or anything. My prediction is that 30 years from now everything that is manufactured, and I mean everything, will be manufactured in a 3D printer.