On the same day I started this series, Tim O'Brien at Sonatype started a series describing the benefits of using a repository manager and saved me a little work ;). He essentially replaced the piece that I've been working on this past week, but he likely did it better (and I still learned tons while researching and writing). Here are links to his articles:

• Benefits of a Repository Manager: Part I
• Benefits of a Repository Manager: Part II – Caching and Collaborating
• Benefits of a Repository Manager: Part III Continuous Build Deployment
• Benefits of a Repository Manager: Part IV Deployment
• Benefits of a Repository Manager: Part V External Partners and Vendors
  

Further pieces to this series are still in the works, though I'll need to do some refactoring and may change the format of some of them to comment on his series with details specific to Javascript, since I'd be repeating much of what he says anyway.