Before you ask, yes, the image at the beginning of this post is a conductor, not a composer. The open source PHP package management Composer has a conductor as its official logo, and who am I to argue? An image of somebody scribbling away on sheet music may have been less compelling. A harmless sleight of hand.
As I work on more and more Drupal 8 sites, I am becoming convinced that given enough time, nearly all Drupal 8 sites will need to be managed with Composer. I think that's kind of a big deal.