Life naturally categorizes the relationship you create and maintain over the years: family, friends, co-workers, college buds, ex's, etc. Social media is no different. And, because folks like myself tend to collect people over the years, our social networks get very busy, loud, crowded and overwhelming at times.
It's nearly becoming unmanageable. I can't possibly following 1000+ people on Twitter and really know every single one of them. Add on Google+, Facebook, flickr, et al and all of a sudden, you have an ecosystem of people that fit into one category or another.
This is why lists, circles, groups, etc. are so important in keeping tabs on your social hive, as I call it.
Your social hive is all your groups together, working for you -- creating content for you; asking you for help; seeing your advice; looking to read your content, etc.
When creating social strategies for brands, managers or agency types should think about building community in this way. How can you segment the target audience by categories, which when brought together work in tandem for you, your brand or your clients.
Each category has a specific need. They each serve a purpose. But, again, collectively, they can hum along like a social hive -- creating and taking action.