When you have a team of people who do the same work, if there is one person who consistently writes half as much code as the rest that could be a reason to look deepen into that person's performance. When you have for example a new project, you split up all task to be done in several-hour long chunks and you assign those chunks to all team member in a way so that the work is comparable (roughly equal parts GUI, algorithm implementation etc.), it's reasonable to expect that everybody would product about the same amount of code (or checkins or similar). If someone is 2 or 3 standard deviations from the median, that says something. Maybe it says something about that person, maybe about the way tasks are allocated, either way it says something.