Automatic Updates (AU) is designed mainly to keep client computers up to date with critical security patches. While AU is a feature of Windows server platforms also, it's generally not a good idea to use AU by itself to patch your servers. Why? Two reasons:

• Patches should always be tested before being applied to mission-critical servers.
• Patches often require a reboot after being applied to servers.

So while turning on AU on your servers and just letting patches be automatically downloaded and installed at 3 am, it can cause service interruption to clients in a 24x7 environment, and it has the potential to blow up your server should the patch break something unexpected.