ROR uses a concept called convention over configuration. This concept came about as a result of the emergence of best practices over the years. It allows for quick setup of an application.
Since the framework is laid out for you, you will not spend time creating it and can focus other aspects of your application. It offers a level of productivity not found in other web frameworks. The rails framework learning curve may appear large and looming at first but knowing that when you move between rails applications in convention, you realise you do not have to relearn how it all connects since it is the same.