It enables 802.1x authentication (aka port based authentication).

http://www.ieee802.org/1/pages/802.1x.html

You need a WAP that supports 802.1x, or another service or AAA server that will utilize it. If you're not running a win2k3 domain, then I don't think there is a lot of options for the home user.

There's a lot more to it, but in a nutshell, 802.1x authentication is meant to protect the network and assets at the port level. Not port as in logical TCP ports, but port as in RJ-45 socket ports. The idea is, if 802.1x authentication is required and enforced, anyone plugging into the network would not be able to access any (or perhaps only a short predetermined list) resources until they properly authenticated. I believe the 802.11i (and/or other) security standards for Wireless may be based on 802.1x, or borrow heavily from it.

It's been awhile since I did much with this though, my details could be off. The link should help provide some insight.