Firewalls give you much better security from outside crackers (malicious users). That is the purpose of firewalls. You can control which TCP ports are open on your server to prevent crackers from hunting for ways to break in. If you want, you can specify what IP addresses (physical machines) are allowed access to the server. And many other features of advanced firewalls.
The downside to firewalls is that they cost a little money and require careful set up and maintenance. If you want to run a top-quality network, however, they really are required.
This was first published in June 2001