If you're on a limited bandwidth plan you may want to disable it. BUT while it's true that it uses your bandwidth to distribute updates in a sort of bittorrent peer-to-peer manner, it also allows you to GET updates in this way. So leaving it enabled means the collective of the Internet will help you receive updates much more rapidly as well.
To turn it off, follow these steps:
* Search for “Check for updates” in the Start menu.
* Under “Windows Update” choose “Advanced options.”
* Under “Choose how updates are installed” click “Choose how updates are delivered.”
* Disable the toggle under “Updated from more than one place.”