The Enterprise Vault client can maintain a personal, Vault Cache for offline workers. These are users with offline folder files (.OST files) on their local disks, who use Outlook to synchronize their online and offline folders.
The Vault Cache performs the following functions:
Provides instant access to archived items, even when the user is not connected to your corporate network.
Is in addition to, not instead of, the normal, online archive.
Is useful to mobile users who use laptop computers. Such users are often used to synchronizing their offline and online folders.
May be useful in normal offices if you need to conserve bandwidth or improve performance, because the retrieval of an archived item all takes place on the local computer.