This beautifully edited video may help you understand the potential for printed construction products and systems. This machine is printing ceramics. Still small in size, but imagine it scaled up to produce entire wall panels, building modules, or structures.
"Eran Gal-Or, an industrial design student from H.I.T institute in Holon, Israel built a 3d printer that prints ceramic materials - porcelain, clay & glass. This is a massive 80x80x80 cm darwin style 3D printer, and probably the largest in the world. The printer prints porcelain in a continuous way using a feeding system he developed, which includes a commercial moineau pump and a refilling plunger type extruder."
Video at http://www.youtube.com/watch?v=N1LF14QhNyY, photos and quote from http://www.3ders.org/articles/20120806-israeli-student-develops-largest-3d-porcelain-printer.html