From what I learned also, it doesn't keep someone from using a IP address on the network, it just keeps people from aquiring one. Basically stops the DHCP server from handing a IP off. But if your already connected, or if you set yourself to a static IP, I don't think it does anything to disconnect them.
I know this because I had a friend over and we were messing around, and as I joke I thought it would be funny if I kicked her offline as we were Vs each other in a game. No matter what I did though, I couldn't instantly disconnect her. She was wired though, I was wireless.