You can attach externally referenced drawings stored on the Internet or an intranet to drawings stored locally on your system.
For example, you might have a set of construction drawings that are modified daily by a number of contractors. These drawings are stored in a project directory on the Internet. You can maintain a master drawing on your computer, and attach the Internet drawings to the master drawing as external references (xrefs). When any of the Internet drawings are modified, the changes are included in your master drawing the next time you open it. This is a powerful mechanism for developing accurate, up-to-date composite drawings that can be shared by a design team.