RequireJS - What is the purpose of the "exports" property in shim

What is the purpose of the "exports" property in the shim below? Is it really required?

requirejs.config({
    shim: {
        'backbone': {
            deps: ['underscore', 'jquery'],
            exports: 'Backbone'
        }
    }
});

I ask because it seems redundant - when the module is included in a dependency list, we will specify the exported name again as the function argument:

define(['backbone'], function (Backbone) {
  return Backbone.Model.extend({});
});