@RenderBody is a must in _Layout.cshtml otherwise error is thrown : The "RenderBody" method has not been called for layout page "~/Views/Shared/_Layout.cshtml".

Yes, RenderBody should be included on every layout page, regardless the nesting. @RenderBody works as a placeholder for the engine to know where to drop the content of the view using the layout page. http://stackoverflow.com/questions/18323268/renderbody-and-rendersection-must-be-on-every-child-layout