The most common type of DHCP Relay deployment in IP Fabric is where the DHCP Relay is installed on the Border Leaf.
In this deployment, the DHCP Client broadcasts the DHCPDISCOVER packets through the network. When the packet is received by the DHCP Relay, that node in the MCT pair, that receives this packet, forwards the DHCPDISCOVER packet to the DHCP Server.
Also, since the DHCPDISCOVER packet is a broadcast packet, the devices in the MCT Pair broadcasts these packets to the same broadcast domain from where the packet was received. This could cause flooding in the domain.
The ip dhcp relay disable-flooding command prevents such a flooding. When enabled, it prevents the DHCP Relay from re-broadcasting the received Layer 2 DHCPDISCOVER packet. For more information, see Prevent Flooding of Broadcast Packets from the DHCPv4 Relay Agent.