IMRAD stands for Introduction, Methods, Results, and Discussion, which is the general order in which materials are presented in social and natural science research reports. (Some versions throw in a literature review ahead of the methodology, and tack on a conclusion, references and appendices after the discussion.)
The upshot of the IMRAD format is that the interesting bits all happen at the end—the results are the part that is new, and the discussion finally gets around to talking about why the new stuff is important.
IMRAD is usefully contrasted with journalism’s “inverted pyramid,” in which the new information is presented at the very front of the article, with details coming later, and context provided at the very end.
Both IMRAD and the inverted pyramid are grounded in print metaphors—they assume that readers start at the beginning, and read the text sequentially to the end.
An all-too-common view in the research and policy sector is that the IMRAD report (usually in PDF) Just Is the way that such materials are presented — that the writing of such things is timeless, independent of technology. Any attempt to change the report is met with accusations of "dumbing things down." The job of designers and technologists is simply to transfer the thing into the appropriate distribution channels.
For many—particularly in the social science disciplines that dominate the think tank space—the final form of the academic essay is the IMRAD report.
Nowhere is this more obvious than in the social sciences, where IMRAD and its attendant passive voice verbs are regarded as the sine qua non of research outputs.
A research report probably isn’t the right form most of the time. IMRAD just isn't a structure that lends itself to very many different uses. But a nonlinear, choose-your-own-adventure toolkit won’t be right most of the time, either.
The document is the fundamental unit of information exchange on the web. Research findings are (usually) collected into IMRAD reports that are (usually) formatted as PDFs. Those reports—whether PDF or HTML—are referenced by a single URL and are (usually) categorized via a hierarchical taxonomy.