In theory, 3-D printing is the wave of the future. The ability to print out anything you want on-demand is devilishly alluring. Yet in practice, for the average consumers, 3-D printing as it stands isn't all that useful. Unless you need some plastic trinket the global corporate-industrial behemoth has not seen fit to mass produce, there's probably an easier and cheaper way to get what you're after.
But that's not true for everyone. For astronauts in space, getting anything is a pain. It cost, all told, around $1.2 billion per trip to launch the Space Shuttle. Even SpaceX's new unmanned Falcon 9 spacecraft will cost $57 million a shot. And if you need something in space, you're looking at a few months wait for the next resupply mission. In space, nothing is cheap or easy. That's why the ISS may be one of the best places for a 3-D printer.
As early as next week, NASA and SpaceX will be sending the first 3-D printer to space. NASA:
Researchers hope to show a 3-D printer can work normally in space and produce parts equitable to those printed on the ground. [The printer] works by extruding heated plastic, which then builds layer upon layer to create three-dimensional objects. Testing this on the station is the first step toward creating a working "machine shop" in space. This capability may decrease cost and risk on the station, will be critical when space explorers venture far from Earth and will create an on-demand supply chain for needed tools and parts.