The killer app for open-source hardware is scientific components and apparatus. It improves accessibility and repeatability, and can deepen your understanding of experimental results and error budgets. Check out Open-Source Lab by Joshua M. Pearce [1], as well as his lab's website [2]. Also check out the Gathering for Open Science Hardware [3].
[1] https://www.elsevier.com/books/open-source-lab/pearce/978-0-...
[2] http://www.appropedia.org/Category:MOST
[3] http://openhardware.science/