According to Apple’s Support page, the Snow Leopard update contains fixes for several small issues, including transferring information, settings, and applications from your Snow Leopard machine to a Mac running Lion; networked printers that automatically pause and then cancel print jobs; and a system audio short when using HDMI or an optical audio out cable.
You’ll need to be using the latest version of Snow Leopard (10.6.8) to run this update; otherwise, you can upgrade using Update Combo v1.1, which includes the above fixes as well as those addressed back in June with OS X 10.6.8’s initial release.
Snow Leopard Server users have two similar patches available, a supplemental update for those already running 10.6.8, and Server Update v1.1 for those needing to update to the latest version. The patch fixes a server-side performance issue.
You can download the patch from your computer’s Software Update utility or from Apple’s Support Downloads website.