Now, with the multitude of different devices, the question is no longer just that, now you need to know how a website looks on different types of screen sizes, whether it's a computer, a tablet, or a mobile phone. That's where the importance of responsive web design, RWD for its acronym in English, comes into play.
To become familiar with responsive design and how it can help your site, you need to understand what responsive web design is.
Responsive web design is a way of designing and coding a website that makes every element of the site's navigation adjustable based on screen size. Text, images, and videos all move into their appropriate position based on how much viewing space is available. Where there once was a mobile and desktop version of the same website, now with a responsive design (RWD) you only need to have one website.
Failing to “get with the program” and not applying adaptive design can, in some cases, pose a problem that directly affects our website and, therefore, an error for our online promotion or online marketing interests. This could basically translate to a reduction in the number of visitors who opt for mobile device navigation. This, in turn, is intrinsically linked to our website's SEO positioning.
Choosing this type of design for our website is synonymous with ease, representing a great success that allows us the following advantages:

There are certain aspects to consider when defining this design, such as ensuring that block content has a logical and readable distribution for all devices.
If we decide on Responsive design, we should know that there are different emulators or programs that offer us a preview of what our website would look like with this new design.
Saves time and money.
The need to develop and maintain two websites disappears; a responsive site will save on total development costs. However, the cost of a responsive site is higher, but the total cost is significantly lower, as there are fewer changes that need to be implemented when your site can react appropriately regardless of who is viewing it or on what device.
More and more people are viewing websites from mobile devices. Anyone still trying to do things the old way is just fooling themselves. Responsive websites have become the industry standard, and website owners don't want to be left behind.
There are so many different screen widths and lengths when it comes to mobile devices. You can't build a static site and expect all these devices to display content in the best possible way. The best thing about responsive websites is that no matter what device the user is looking at your site with, the site will always display in the best possible way.
Responsive design is about providing the user with the best possible experience, no matter what device they are using. It's about making it easier for the user to navigate, explore, and understand so they can get exactly what they want from a site. If your site is difficult to view on mobile, the user will abandon it in less than 3 seconds and go to one of your competitors.
A Responsive site is, for now, the present and the future. No matter what type of mobile phone you use, Apple, Samsung Note, your site will look good on all of them.
Source: Zuiton.com / Ecomputer