If you are using your Cisco PIX firewall to protect a set of services based on source IP address then you might have defined a number of object-group sets and it can be hard to scroll through these when using the PIX command line interface.
By using the id parameter you can show the members of a single object-group:
show object-group id pop3
network-object host 1.1.1.1
network-object host 1.1.1.2
network-object host 1.1.1.3
network-object host 1.1.1.4
network-object host 1.1.1.5
network-object host 1.1.1.1
network-object host 1.1.1.2
network-object host 1.1.1.3
network-object host 1.1.1.4
network-object host 1.1.1.5