What Happens if routing is not there in MVC ? What is the Importance of Routing in MVC ?

public static void RegisterRoutes(RouteCollection routes)
 {
     routes.IgnoreRoute("{resource}.axd/{*pathInfo}");

     routes.MapRoute(
         name: "Default",
         url: "{controller}/{action}/{id}",
         defaults: new { controller = "Home", action = "Index", id = UrlParameter.Optional }
     );
 }