It could be used to implement a pure server-side MVC Web 1.x style site.
However, it's also a command line processor. So you can load up all your libraries that you use in your WWW server application and do some long running operation, like importing a million records into your database, add watermarks to all the images in a directory structure, etc.'
This has nothing to do with code running in the browser, although you could share entire .js files between server and client. I could see having a Validator class that could validate form input on both sides of the connection, for example.