title: RouterModule.forRoot(ROUTES) vs RouterModule.forChild(ROUTES)
body: <p>What is the differences between these two and what are the use cases for each?</p>
  <p>The <a href="https://angular.io/docs/ts/latest/api/router/index/RouterModule-class.html" rel="noreferrer">docs</a> aren't exactly helpful:</p>
  <blockquote>
  <p>forRoot creates a module that contains all the directives, the given
  routes, and the router service itself.</p>
  <p>forChild creates a module that
  contains all the directives and the given routes, but does not include
  the router service.</p>
  </blockquote>
  <p>My vague guess is that one is for the 'main' module and the other is for any imported modules (since they would already have the service available from the main module), but I can't really think of a use case.</p>