Responsive web design allows eCommerce websites to work well on any device by automatically adjusting the layout. It provides users with a better experience across different screens like desktop, laptop, tablet and mobile. Some benefits of responsive design include improved brand reputation, increased traffic and conversions, reduced bounce rates, lower development and maintenance costs, and better search engine visibility. The document provides examples of responsive sites and statistics on increasing mobile internet usage to argue that responsive design is important for eCommerce websites.