What is responsive design and why should I use it?

Responsive design is what most good websites use these days. It is more efficiant, better looking, and more search engine friendly than going either desktop only or seperate desktop and moblie sites.

More effecient

With responsive design, we plan the content and design the layout (more or less) once. The server serves the same thing to everyone with no redirects to slow them down or mess up what page they are suppoed to be going to. On the browser side, we can set it up to request slightly different images to save bandwidth, but on the server end and most parts of the design, we don't have to duplicate the effort, and everything can be effectively cached and server correctly by a CDN or other cache. This will all get better as some of the new CSS gains support - but it's pretty effective today.

Better looking

Responsive design is not typically broken into the old two distinct versions; desktop and mobile - instead it may have five, ten, or even more different steps along the way. This means we can take advantage of a very large screen, while fitting on an ultrabook, a tablet, and all the way down to a phone - and looking like we specifically designed for each. We can even handle making the site look different when you print it out (showing link URLs for example).

More search engine friendly

Responsive web design has a few benefits when it comes to search engines. First, Google - and probably others - now use a site's mobile-friendliness as a significant ranking factor (for mobile searches). Additionally, it guarantees that there are no duplicate content issues, as each page only exists as one version of itself. But possibly most importantly, it means that there is no issue with poor or incorrect redirects from the desktop version to the mobile version - see this XKCD to see what a bad redirect can do.

Downsides

There is really only one, and it can be fixed, but usually isn't (even by us): With responsive design, what version of the site a user sees is determined by us and can't be overruled. With a good responsive design, this is not very important, as the page has all the same content and only a different layout. But if for any reason the content is different, or if they just prefer the layout of the desktop site, they are left without a way to get there.