Hello Brian
CBAC is part of what Cisco calls the Cisco IOS Firewall feature set. It’s essentially a subset of firewall functionality that is made available on Cisco IOS routers. You can find out more about this feature set here:
The purpose of this feature set is to enable security features on an already existing Cisco IOS device, without the need to purchase a purpose-built firewall. I would say it is a feature of convenience and should be used sparingly. Some may call it a “poor man’s firewall.” It does have limitations, which are detailed here. In any case, it should be used sparingly and only in low-risk situations, such as a small office with no mission-critical network services or data.
For proper security, a separate purpose-built firewall should be used.
The technology is indeed old. The link I sent you above is almost 20 years old, but it is still an active feature in Cisco’s IOS 15M&T releases, so it’s still usable today.
I hope this has been helpful!
Laz