Laura,
It will enable the ap to advertise to the directly attached switch information about its self.
https://en.wikipedia.org/wiki/Link_Layer_Discovery_Protocol
How this may help you, if you are looking to find devices and where are they attached on your network. Typically a switch, for example, will have some commands to show connected devices learned via LLDP. As Timo pointed out it can also be used to negotiate power draw when the ap boots up.
Doug Hyde
Director, Technical Support / Extreme Networks