Rather than having to do an install and hit Next, Next, Next, Cancel (damn, wrong one!) you can pass the installation routine all of the settings it needs.
This is useful because you get reliable, consistent builds across hardware types. Sometimes you will need to add in the additional drivers needed but once thats done it's actually a really nice way of performing an install.
Another nice feature is the ability to slipstream service packs into the install media. This gives you the ability to deploy the software with the service pack pre-installed.
I always spin off a copy of the install when applying a service pack. This way I can roll back to a previous unattended installation if needed.
Recently, Micrsoft has added the ability to /integrate patches into the install. In theory you can install a new machine fully patched before it even hits the network.
In Theory.
In Practice someone at Microsoft needs to test this.
Recently I tried this on Windows 2003. The service pack slipstreamed and installed with no problems.
Integrating the patches also generated no errors but when running the installation you'll get the following error:
This DLL is used by MS05-039
So, Now we have a problem. Do we ignore the file? Well, you can't do that because you will still be unpatched so all you can do is NOT integrate that patch into the unattended files and this means when the machine starts up it will be missing patches.
Annoying and unnecessary.