Research through Design is one of the creative research methodologies in the field of HCI. Zimmerman, Stolterman and Forlizzi have investigated this methodology by interviewing 12 pioneer HCI researchers.
They argued that a new artifact created by a designing process (products, environments, services, and systems) is a new type of implicit contribution. Also, they have claimed that RtD can result in conceptual frameworks and philosophies. Moreover, RtD forces the researcher to focus on the research of the future instead of on the present or the past (View Full Article).
As a junior member of the HCI community, I believe that RtD is critical for the advancement of HCI because it allows the researcher to think outside the current boundaries and create new concepts and frameworks. We need the creative constructivism of Design through Research methodology. Without a design-based approach, a researcher may not find a solution that dramatically enhances the answer to the problems.
If you are interested in RtD, you may find this book helpful.