Anyone who knows me knows that I can argue both sides of a topic with equal fluidity. This is a skill I picked up from my father who was legendary for asserting a position and then explaining (to anyone who would listen) all the reasons why his deeply held belief might, in fact, not be right. In my response to a comment about my posting about PM as technology luddites I made the assertion that PMs should have some level of subject matter expertise. This is a definitely something I believe in quite passionately but like most things there are exceptions. Based on my own experience the definition of what subject one needs to be an expert in changes depending on one’s role on a project or program.
Once upon a time, in a world long past, I was a program manager on the final stages of a large custom costing and planning system. I knew the industry, I knew the costing function (at least at a high level) but the truth is I could have known absolutely none of those things and still have done my job. The only subject matter expertise I needed for that job was 18 years of management experience in leading teams and keeping senior management happy. In fact I can safely say that all of my program management assignments never required me to get involved in the details of what we were delivering; I had project managers who did that and they were more than good at their jobs.
So if I didn’t need to know anything about what we doing specifically did I still need to know something about software? I think so, but my opinion on this topic is a little less strident and a little less sure. I believe the answer is yes because if you aren’t an “insider” then unless you have some other claim to charismatic leadership, the team probably won’t have enough confidence in your abilities for you to be an effective leader.
So bottom line, I think how deep your knowledge of the “product of the project” has to be changes with your role on the project/program but even when you don’t have to know anything about what you’re delivering you still need to know how to inspire confidence in the people you’re leading and that generally means being considered “one of them” by virtue of prior experience.