It's relatively straightforward. Take a look at what Pingdom tells you it does when the site loads:

http://tools.pingdom.com/fpt/#!/cnYAuq/https://news.ycombina...

5 requests, Total size 12.6kB, total time 661ms. 1 request for the content, 1 for css, and then 3 gifs, all from a single domain (so just one DNS request). If you look at the profile, 47% of the time was spent doing that one DNS lookup, so subsequent requests will be even quicker (plus caching will handle those gifs just fine)

That's almost no work for the end client to do. No javsacript for the client to download, parse and process, just straight content to render and done.

The reduced request count is especially important when it comes to the mobile experience, where bandwidth might be great, but latency is terrible. Every request you have to make to render a page significantly impacts the loading time (HTTP2 helps here). Along with trying to reduce the number of resources being loaded on the screen, it's especially important to reduce the number of domains you're getting them from so you keep the DNS queries down.