Core Benefits of Responsive Web Design
A "responsive" website means that web pages will render in optimized fashion according to the width of the user's browser.
By using a technology called media queries, your website can bend and stack into optimized versions for iPhone, Android mobile devices, Android tablets, iPad, iPad mini, Windows Phone, and more while all of your content and URL's stay the same. This last part is especially crucial for those concerned about Search Engine Optimization (SEO).
It gets expensive making apps that run native on iOS, Android, and Windows -- along with other devices such as Blackberry. You can reach them all with an HTML5-valid, responsive website.
How do you make a website "responsive"?
Your Drupal website gets designed with a special theme (design layer) that defers to custom theme templates per width range. For example, while there is one master CSS style sheet for desktop sizes, there are modified versions of CSS style sheets for different sizes: 0 - 240 pixels (iPhone, other smart phones), 240 - 320 pixels (iPhone in landscape), 320 - 480 and 480 - 768 (tablets), 678-992 (smaller laptop screens), and 992 and above for desktops. There are also options to customize the layout for older versions of Microsoft's Internet Explorer. (IE 8 and earlier are notorious for causing web developer nightmares.)
Because of the cascading nature of CSS style sheets, sometimes CSS tweaks for the master style sheet or sub-themes can wreak a little havoc or throw things off, but eventually it gets dialed in. The more content loaded onto the site, the easier it is to get the design into solid shape(s).
A well-designed responsive website will always provide usable navigation and readable content for the user, no matter what device they are using. It will be HTML5 and XHTML valid, load very quickly, and also be ADA compliant.
New Superclean websites are now being designed as responsive, and existing clients are encouraged to upgrade to responsive for their next big website refresh. There are many good reasons for doing this, and as far as we can tell there is no reason not to.