Why controlling Source IP address on a Firewall?

[Santi Ribas <santi @ browns . co . uk>]

If the Source IP address is easily spoofed, why implement Source IP
Address control in a Firewall?

The only difference I see is that by controlling it, a hacker will
probably need to check for TCP Sequence Prediction, create a deny of
service to the real client and change the source IP address of the
packet.

Is that the reason??

-- 
Santi Ribas