The benefits of using CSS (Cascading Style Sheets) in web design include enhanced visual presentation, improved site performance, and greater design flexibility. CSS allows developers to separate content from layout, enabling easier updates and maintenance. By using stylesheets, designers can define styles for multiple pages simultaneously, ensuring consistency across a website. Additionally, CSS supports responsive design techniques to ensure compatibility with different devices. This can improve the user experience by making sites more visually appealing and functional, potentially increasing visitor retention and engagement.