There are many sites that were developed in the distant past, when mobile phones were still able to send only SMS messages, make ordinary phone calls, and many of them do not have a version of their site for mobile phone screens. Today, the mobile phone industry, or how to put it right - smartphones, is constantly evolving. Smartphones are a full-fledged computer, with multi-core processors, and a large amount of RAM. Smartphones differ from personal computers only in mobility and screen size.
Sites with responsive design, automatically adjust to the screen size of any device, which allows users to conveniently scroll through the site without manually reducing the page size, as was done before, and this is convenience for users, which is very important.
Responsive design provides not only usability of the site, but also technical advantages. For example, a regular full-fledged site weighs a lot, which means it will take longer to load on mobile devices, which will not have a favorable effect on traffic, and a potential client is more likely to leave such a site than wait until all the materials on the site are loaded. And on sites with responsive design, you can lighten the size of the mobile version by disabling unnecessary modules, removing voluminous photos and video materials, which ultimately will lead to fast loading of the site. Of course, you ask - why should I disable this or that module, or remove a video or photo from the site?
First, users visit sites via mobile devices in order to quickly get the information they need. Often this is a list of services and contact information. For this reason, there is no need to load the mobile version of the site with unnecessary information. "Brevity is the soul of wit". As Anton Pavlovich Chekhov said. For users of the mobile version of the site, clear, concise information is enough to be interested in the services or goods presented on the page. So, you can safely turn off everything that is unnecessary for the mobile version of the site, and leave only brief information.
Second, sites with fast loading are well received by Google and Yandex search engines. Websites are created in order to find clients, reach out to an ever-increasing audience, potentially interested people. Where to find such people? Nowhere. They themselves will find you. Thanks to search engines. And in order for the search engines to be loyal to your site, in order to better rank the position of your page for certain key queries, you must follow the rules of these search engines. Fast loading of the site, the presence of a mobile version of the site, the information content of the site, these are the rules - recommendations from Google and Yandex to make your site competitive among thousands of other sites.
The third is to create a comfortable environment for mobile users. Fast loading, concise and informative content. All this is good from the point of view of search engines and marketing, but do not forget that user-friendliness is one of the important factors to keep a potential client on the site. And for their convenience, it is worth including in the mobile versions such tools as: a callback, online chat, the company's location on an interactive Google or Yandex map, answers to frequently asked questions, and social buttons for quickly navigating to the company's page on social networks.
In conclusion, I can say that sites with responsive design are now gaining great popularity, along with the development of the mobile device industry and the available Internet using 3G and 4G standards. Therefore, it is very important that your site is already adapted to the screens of various devices.