My thought is it's a way to keep track of your favorite shops by seeing their activity feed in your Activity Browser (similar to Facebook). So, if someone puts you in their circle it's a huge compliment because they want to see what your latest posts are, who you favorite, and where your work is being featured (i.e., treasuries). I personally love it because it means people want to know what my shop is doing ;o), add away please!
hugs,
brienna