Comments are the vital part of communication with the audience. It fits for a lot type of websites starting from blogs finishing with e-commerce. Metalsmith is a static site generator, that means (in most cases) that developer doesn’t want to have a database and other back-end infrastructure to implement commenting functionality. But it not says that you can’t add it.
Few times I started to develop my blog locally, but only this implementation came into production. Previously I tried few CMS variants, other static site generators, but stop my decision on Metalsmith. I’ll tell my story and try to argue why you might use Metalsmith for your next project.