Architecting a VMware NSX Solution : Design Considerations : 4.13 NSX Logical Switches : 4.13.1 Multicast Mode : 4.13.1.1 Design Considerations
   
4.13.1.1 Design Considerations
Requires IGMP and IGMP snooping configurations throughout the physical network which adds complexity to the configuration and is not always available on the network.
Multicast IP addresses must be reserved on the physical network.
The use of multicast mode reduces the overhead incurred on the source host VTEPs.