Besides the legal status of IP logging in Germany or European Union, I am with Kirby and would prefer to have the option to disable IP logging.
Data which is not in my hands/databases can't be stolen, copied or what ever in the case the server or forum gets hacked.
And I don't need these information, so why should I store it?
The same with Email addresses, I don't want this information after successful confirmation of the registration.
The lesser personal data I have, the better.
During the last attacks on my forum I had to defend the availability of my forum from server side (Data Center routing reconfiguration, Cloudflare + Bitninja), the storage of IP addreses wasn't helpful.