Explain EncodeURL in portletsResponse?

The PortletResponse interface provides an encodeURL method to let portlets encode
portal server or portlet container–specific data (like session ID) in the URL. Such
URLs can refer to resources like JSPs, servlets, images, and static files (like JavaScript
and CSS) in the portlet application

URLs referring to resources within the portlet application must be
encoded to ensure that the portlet application is portable across different
portal servers and portlet containers. We don’t need to encode URLs that
refer to resources outside the portlet application.