You create a site collection to host sites that are going to have something in common. For example, the sites might be in a common administrative boundary or share common branding. The site collection might be created to house all the sites and content for a business unit. Or, a single site collection might have become too large to manage, and it must be split into smaller ones. Lastly, some site collections are created exclusively to host specific SharePoint 2013 functionality, such as Enterprise Search Center or to host My Sites. Site collections are a way of organizing sites for a common purpose.