..pay for themselves. For starters they can print half their own replacement parts!*
http://www.computerworlduk.com/news/infrastructure/3461835/3d-printers-can-pay-for-themselves-in-under-a-year/
*yes, even some electronic circuits!
http://www.computerworlduk.com/news/infrastructure/3513710/this-3d-printer-technology-can-print-a-game-controller-electronics-and-all