I always found it to be a real PITA... It felt like a parallel system to file permissions, which meant I had two things to configure instead of one and I never really saw the purpose. It seemed like it could be more granular than the default, but if it did anything more than that I never learned about it

Granted, I'm a dev, not an admin. I go back and configure the firewall after I shut it off because it was in my way... Eventually