Should firewall policy should only be concerned with inbound (ingress) traffic?
Simply, NO.Outbound traffic is also important because outbound protection alerts you about doubtful attempts that may try to connect to computers outside your network from within the network. There are legitimate processes on your computer that need to connect to outside machines for different reasons like, for updating, mail services, chat services, etc... But if there is a malware on your computer (Firewalls can't protect you from two things.1. Firewall by-passing.2. Internal threats ) you should be able to prevent it from connecting out to send data or hacker invites.Traffic should be monitored (and even filtered) for connections to odd port numbers. Malware already embedded in your network may attempt to spread or contact a home server with gleaned security data.A quality firewall should allow you to retrieve logs sorted by host name, ip address and port numbers so that spot checks would reveal anomalous in and outgoing activity.