Microsoft Windows Software Update Services, or WSUS, is an application that allows group policy driven automatic deployment of Microsoft product updates. It is usually a given when planning a WSUS deployment that you let it reside on its own dedicated server. This is due to the sheer size of all the Windows services packs and hotfixes residing on the server as well as the large amounts of hard disk I/O experienced when deploying these updates.
This being the case, the common downfall in planning a WSUS deployment is not underestimated the physical server requirements, but rather the bandwidth requirements of the installation. WSUS was designed with these type of environments in mind and allows for a distributed environment in which one WSUS server acts as the master and all outlying WSUS servers act as slaves.
In any situation where you have a significant number of clients connected to your main network segment via a slower link you will want to consider this master-slave setup in order to be able to effectively deliver Microsoft updates.
For more information on setting up WSUS in a distributed environment, see the Microsoft WSUS deployment guide at www.chrissanders.org.