This was a phrase I heard from a writer years ago when we were concepting ideas for a small, nimble and effective company needing to promote themselves in a sea of bigger companies vying for the same clients. It really sums up how you don't need a giant agency to hit your marketing targets.
The article below points out some major points in selecting a smaller agency vs. a larger agency.
http://adage.com/article/small-agency-diary/small-agencies-crush-big-agencies/238476/