I saw the following line while studying about Global policy on PIX:-
"Security Appliance handles the traffic which enters the device and Ignores the traffic which leaves the device"
If we take example of IPS.Here whether Ignore means that the security appliance will drop the packet OR it will just pass the traffic without any check.
i.e. the security Appliance will do IPS inspection when the traffic enters the device and the device just pass the traffic(without IPS inspection) when leaving any interface.