Why do you need the prefix "www"?

The “www” prefix has remained since the time when various “parts” of the site were hosted on separate machines: Apache server on one computer, mail server on another, FTP on the third. Each computer had its own IP address, but the same domain name. Within this domain name, computers were differentiated by the service provided (“machine name”). Thus, server names began with a “machine name”: www. Domain.ru, mail.domain.ru, ftp.domain.ru. Now, when all services are located on the same machine, the prefix “www” seems to be “antiques”. However, many large sites ( w3.org , google.com , microsoft.com , etc.) use only the domain with “www”.



In one of the articles , the following reasons are given why it is necessary to use one domain (www. Domain.ru or domain.ru), referring to another should lead to redirection:

• Many search engines perceive www. Domain.ru or domain.ru as different sites, possibly with different PRs.
• Since www. Domain.ru or domain.ru are technically different sites, PHP sessions cannot be transferred from one to another.

Question. What do you think, why now use a domain with “www” as the main one ?