If software development is an assembly line, then unclear roles is a real problem (see illustration.) You don’t know who is supposed to tightnen the nut. It might be tightend twice, it might be tightened once, but one thing is certain: The variation in the tightening will slow the line down. So one of the ideas in traditional process improvement is to clarify roles and responsibilities, job descriptions, and so on. (Or, in other words, to “decrease the variability in the process”, a line right out of the PI literature.)
I am a bit dubious of that position, but we’ll get to the why tomorrow. In the mean time, what do you think?