Álvaro Sánchez-Mariscal discusses developing single-page applications (SPAs) using Grails and AngularJS, highlighting the limitations of traditional Grails MVC architecture for large projects, such as slow rendering and challenges in deploying changes. He emphasizes the benefits of SPAs, including improved user experience, faster performance, and easier team collaboration. The document outlines approaches to leverage Grails for SPA development by utilizing REST capabilities and integrating with AngularJS for a more responsive application structure.