Often people think that clutter is about stuff when really, it boils down process and priorities. In that regard, getting rid of unnecessary stress is one of the goals of uncluttering your life.

Also, it isn't about filling your head with useless data -- it's about improving the quality of your interactions with people, making life easier and better for both parties.

Or, to consider from a crass perspective, humans are wired for reciprocity (viz Cialdini's "Influence"), so as the article points out, you'll get more favors, preferential treatment, and marketing opportunities from people who feel they have a connection with you.