Multisite mode is designed for deployments with multiple physical locations. Installing a Single Sign-On instance at each site allows fast access to local authentication-related services. Each Single Sign-On instance is connected to the local instances of the AD (LDAP) servers and has its own database with local users and groups. In each datacenter, you can install Single Sign-On in standalone or clustered mode, pointing to the identity sources in that location.
Multisite deployment is useful when a single administrator needs to administer vCenter Server instances that are deployed on geographically dispersed sites, with separate vCenter Single Sign-On instances for each site.To view all such vCenter Server instances from a single vSphere Client or vSphere Web Client, you must configure the vCenter Server instances in Linked Mode.
Hence no difference 