A site-to-site VPN allows offices in multiple fixed locations to establish secure connections with each other over the internet. Site-to-site VPN extends the company's network, making computer resources from one location available to employees at other locations.

A client-to-site VPN allows users in multiple mobile locations to establish secure connections with the company network over the internet. Client-to-site VPN extends the company's network, making computer resources from one location available to mobile employees.

An example of this type of VPN connectivity is a remote user using an insecure Wi-Fi network such as those at a coffee shop, airport, or hotel. To prevent a nearby party from intercepting the insecure communication over the wireless network, the user can establish a VPN connection to the company network.
Another advantage is prevention of data loss/theft. So if a company laptop is lost/stolen all the information are on the servers, not on the laptop.