IP addresses are the identity of your server (kind-of). Giving information about you IP address can be useful to someone that would try to directly attack you.
By looking up your IP address over the internet, one might find information you left there (server config files, availble services, hardware ...) that can be use to passively gather intel on your potential vulnerabilities. This can be done because the IP is tied to the information (over forums or others), or because you know tied your own identity to this IP. Then one might get more information by tracking you instead of the IP.
Furthermore, this increases your 'visibility' by giving up a valid target in the open.
IP addresses are indeed public, and intel can be gathered many ways, but this is not a reason to make it easy for attackers to learn more about your infrastructure.