A page’s download time client-side directly correlates to the number and size of files the browser has to download.
For each file, the browser sends a GET HTTP to the server. It waits for the response, and then downloads the resource as soon as it is available. Depending on the type of web server you use, the more requests per page there are, the fewer pages the server can handle. Reducing the number of requests per page is key to reducing the number of HTTP severs needed to run the website, and consequently its environmental impact.
Potential saving: reduced server load, thus minimizing the economical and environmental footprint by reducing the amount of equipment needed (from HTTP servers to application servers and RDBMS).