The document discusses the rise of responsive single page applications. It defines responsive design as building websites that detect users' device and screen size and dynamically adjust the layout accordingly. It advocates for responsive design over separate mobile sites because it provides a better user experience across devices, improves SEO through a single URL structure, and streamlines development and maintenance with one codebase. The document also outlines best practices for developing responsive applications using technologies like AngularJS, Grunt, and Yeoman to automate testing and improve workflow efficiency.