LLDP is enabled by default. That is the Link Layer Discovery protocol in general. The LLDP-MED are the "Media" extensions. You can you LLDP to do device to device discovery. If you have two switches connected to each other, they discover each other via LLDP.
The "Med" extension are for Phones, potenial cameras etc.
When you enable "voice" on a vlan, the switch then sends the vlan information etc via LLDP-MED to the phone so it know for which VLAN to tagg the packet.
Hope this help.
Olaf