There are always two audiences that an aspiring professor must consider: the internal audience (aka the department) and the external one--the wider discipline. It is easy to get so focused on the internal audience because you may constantly be exposed to the opinions of your colleagues that you forget what the standards of the larger community may be.
For instance, at my old job, articles had much value and books were seen as being less valuable (the equivalent of three articles) for getting tenure, so if one paid attention only to the internal audience, investing the time and effort in a book project did not make much sense. However, I sensed that among the wider group of North American political scientists who study International Relations, books have a great deal of value. Indeed, in the discipline of political science, some departments are article places, some are book places and some are in between or more flexible. I knew that the external audience valued books, so to play to that audience, I wrote a book (of course, this is not all strategy as I had a book I wanted to publish).
Why does the external audience matter? Principally for two reasons:
- as part of tenure and promotion processes, outside scholars are asked to write letters evaluating the candidate's contribution, so meeting the external standards is important.
- if one wants to move, then one needs to meet/surpass not just the internal standards but the external expectations.
- a third reason also matters: the internal standards can be subject to fluctuations depending on who is there at a given time (changes due to sabbaticals, retirements, hiring, etc), but the external standards, as a general consensus in the profession, tend to evolve more slowly.
For my department, the best way to proceed is to cultivate a diverse set of skills and approaches. Not everyone has to be writing books, for instance. You can have a few folks more focused on policy audiences even while the overall commitment is to the academic audience. Not everyone has to be a stats guru, but having a few around is a good thing.
The idea is to manage risk a bit but also to maximize visibility and relevance, as these will lead to better reputation, which in turn leads to better students, better hires, more funding, etc. Focusing narrowly on one form of publication, one methodology, or one style can work for some places, but it requires consensus and commitment to that one form (the formal modeling places like Rochester or NYU). The portfolio approach makes the most sense if super-specialization is not available or attractive.