Responsive web design is a technique to writing css code for web design so that it displays efficiently on all devices and creates convenience for the user.
Responsive web design is what makes using webpages on devices easy! It is important that webpages RWD is part of the process of building or editing webpages.
RWD uses different tools to make it possible for website's layouts change between devices on the fly. Everyone has experienced trying to touch a tiny button on a smart phone, this is life without RWD!