I look at it as a means of building the large ships we need for real space travel but yes, the materials could also be returned to earth. The profitability would have to start on earth but the future is beyond.
A while back I was watching a show about colonizing mars and they were demonstrating a full sized concrete printer for standing structures. Obviously its cost prohibitive to carry concrete to mars but a lot of mars has sulfur rich soil. That soil can be heated to 239 degrees to melt the sulfur and then printed into structural walls like concrete. I think people really underestimate the possibilities 3D printing opens up.
http://www.videobash.com/video_show/this-3d-printer-can-build-a-house-in-20-hours-355491
Large domes extruded in space, and made out of otherwise (in the words of Spock) unremarkable ores (as mineral foams), could be dropped to the surface of Mars. They’d thud into position, and colonists could land nearby and move in.
Choosing the right material could make this idea really cool:
http://en.wikipedia.org/wiki/Sapphire#Synthetic_sapphire
http://techcrunch.com/2013/11/08/why-apple-bought-578m-worth-of-sapphire-in-advance/
http://en.wikipedia.org/wiki/Gorilla_Glass