If you enable multicast routing globally, then you should also enable multicast routing (using the ip pim command) on all Layer 3 interfaces on which you anticipate receiving IP multicast traffic. This command causes the packets to be sent to the process switching level to create the route entry. If you disable multicast routing on the RPF interface, the entry cannot be created and the packet is dropped. If the source traffic rate exceeds what can be handled by the process level, it can have an undesirable impact on the system. For example, routing protocol packets, such as EIGRP hello packets, might get dropped.
