Not only is WordPress the leader when it comes to website management for small to medium businesses, but they have also created ways to make it easier for the user to build their search engine optimization.
Creating multisites allows users to create a network of sites under one domain that can share the same plugins and themes. Such individual sites in the network are virtual sites; they do not have their own directories on your server. Instead, they have separate directories for media uploads within the shared installation, and they do have separate tables in the database.
Users can create a “super admin” with overall network control, and from there they can produce as many separate websites as they please, all with their own unique moderators and users. Or, the user can simply use the multisites for their own purposes with no other end users.
Examples of multisites can be a main WordPress website about, say, travel. But the user wants to add a secondary or “child” website on the same domain and WordPress installation about traveling specifically to Europe. The user would enable the multisite function and create a site that is tethered to the original travel site but with different content, images, and meta data.
The best part about creating multisites is that they easily become a structural advantage for your website’s SEO. While subdomain structure has been seen to be treated differently than subdirectory structure, it must still be understood that WordPress’s multisite function is not appropriate for all companies, and nor does it strictly become your website’s only SEO structure advantage. However, when combined with a comprehensive SEO strategy, multisites can become the sharpest tool in a business’s arsenal. But why is that?
Source: https://www.business2community.com/seo/wordpress-multisite-can-structural-advantage-seo-0812406#!ANNOw