For different reasons. If your site is an eCommerce site, then registration allows customers to save and reuse data like name and shipping preferences. If you have a site for an organization, then taking registrations allows you to have members’ only information available on the site that is protected from the general public. Members can see files, pages, and even communicate with each other through the site securely. For businesses, registration allows you to provide customers access to appointment scheduling, customer support systems, discussion forums, or other benefits.