you act like a hub, bridging two networks together, as opposed to a router, where you route between the two (ICS is more like a router).
i.e. you have wired internet access to your PC, and want to bridge that to your wireless network. I don't know if this would work with an unwired AP or not, but in theory it would. I use it to bridge my AP to the network through my box, when I didn't have a hub and was too lazy to dig one out. So it went Modem->net 1 on Computer Bridging connections, out net2->AP. I had 2 live IP's and wanted to be able to use them for some reason.