VPNs enable a remote user to securely connect to a private network or server over a remote connection. To the end user, it is as if data sent is being sent over a dedicated private link. Another common usage is for network-to-network communication. For example, a branch office of a corporation may need to connect their local network with the network at corporate headquarters. In this case, the internet is logically equivalent to a WAN. In both cases, those using the VPN benefit from the fact that the connection is implemented as an encrypted tunnel. This enables end users to use the public internet as a private tunnel for a virtual point-to-point connection.
As noted earlier, private WAN circuits were the only way of connecting to a private network securely before there were VPNs, and in some cases, such private circuits may still be the only way to meet bandwidth...