Public IP addresses are used for Internet communication, including Azure public-facing services. They allow Azure reserves to communicate with the Internet and with Azure services that are accessible to the public. Until you unassign the address, it is committed to the resource. When you use a VPN gateway or ExpressRoute circuit to extend your network to Azure, the private IP addresses are used for interaction within an Azure Virtual Network (VNet) and your on-premises network. Every device on the same system has its own private IP address.