It could still be good practice to minimize all data when it doesn't serve a purpose, and I can't think of a reason not to delete the last byte of an IP address (except possibly in an internal setting where all clients are from the same subnet).

Personally, I don't see much of a problem when my IP is stored somewhere since you'd need a reference, but others have apparently thought more about it and want it to be anonymized.

(I've now come up with scenario: If you have access to multiple such sets of data, you could connect accounts from different systems. I. e. when the youporn logs leak, someone could tie the data to your HN account etc.)