Other than providing questionable demographic value I don’t think they’re important for members that are not a problem. But for spam, most definitely, at least for a while. Not that every IP used by a problem account means that every account using that IP is also a problem. But I have observed that there are problem IPs, or more correctly IP blocks eg. #-#-#-34 to #-#-#-38, that I would be amazed if any of the accounts registering from those IPs were not problem accounts. Having record of those IPs can be a big help in limiting the amount of spam problems.
That makes sense. Thank you