The attack works by forcing legitimate MAC table contents out of the switch and forcing a unicast flooding behavior potentially sending sensitive information to portions of the network where it is not normally intended to go.
The intention is to consume the limited memory set aside in the switch to store the MAC address table.
[1] The effect of this attack may vary across implementations, however the desired effect (by the attacker) is to force legitimate MAC addresses out of the MAC address table, causing significant quantities of incoming frames to be flooded out on all ports.
After launching a successful MAC flooding attack, a malicious user can use a packet analyzer to capture sensitive data being transmitted between other computers, which would not be accessible were the switch operating normally.
MAC flooding can also be used as a rudimentary VLAN hopping attack.