According to Valve, this feature is particularly useful for multi-user Steam households, dorms, LAN parties, and any other situations where users may have limited bandwidth or data caps. After installing the new software on the devices, Steam will first check if it can transfer a game installation or set of update files over the local network before contacting a public Steam content server. If one of the devices involved in the transfer is disconnected from the local network, Steam will download any necessary files from the internet.
