Mark is right – that is certainly the primary purpose of the rule, but it is just a start.  When you think of it as a way to segment community by a particular kind of behavior, you’ll quickly recognize that there are other behaviors that are worth examining similarly.  Call it a “contribution” behavioral segment, since it is is based on how much each visitor contributes to site’s content.  There are many other interesting behavioral segmentations:

• Responsiveness – which of the community’s interactive features do visitors use and how often do they use them?
• Retention – how often do visitors come back?
• Churn – what is the turnover rate for visitors?
• Topics – do people participate equally in the community discussions?

One of these days, perhaps we’ll all know what is normal segmentation for various types of communities (e.g., a support community will be quite different from an affinity community).

For deeper insights, compare the different segmentations and look for disconnects.  I would be especially concerned to find disconnects between contribution and the first two examples, responsiveness and retention (my “R&R” of engagement).  If the major contributions aren’t using interactive features as frequently as they contribute, that might reveal a design or even more fundamental problem with the features.  If they aren’t returning to the site at a normal rate, that suggests trouble ahead.

Side note: I suspect that behavioral segmentation is a good way to find communities within communities.  One of the challenges of community management is to figure out when a group needs to be split into two or more.  Discovering cliques that are naturally following the normal patterns might be candidates to spin out.  In other words, I’ll bet behavioral segments are somewhat of a fractal phenomenon.  And if nothing else, they give us more ways to generate pretty visualizations, eye candy for that next conference or sales presentation.