Google's upcoming Mobilegeddon is pushing latecomers who care about mobile traffic from Google to get off the pot. Its also triggering a lot of great conversations about responsive design, but there's a bump in the road for responsive that isn't getting much airtime... actually its a speedbump. (witty huh?)
The challenge with basic Responsive Design is speed. Because basic responsive pushes the same sized image files to all devices. The device's browser then "scales" the image down to fit - but its the same file size. In today's world of edge to edge photography, these files are large.
In most cases, image files account for 50%-75% of weight of a page.
REsponsive + Server Side (RESS) Speeds Up Websites
While there are many methods of compression, caching, reducing calls to the server to increase speed, one of the most effective is use Responsive + Server Side (RESS) to first take an image uploaded to the CMS and automatically make a bunch of copies at different sizes. Then when the device requests the page, the server sends the photo closest to the screen size of the user. Not only that, but there may be images of elements of the page that just aren't needed by the mobile user for example. In those cases, the server doesn't send it at all.