I can't think of any reason to have someone's IP except to block it in case that participant became too much of a troublemaker.

Several times I was asked to determine if several different posters were the same person in real life and I was able to detect that more than one screen used the same IP, however that was not proof-positive that they were one and the same person.

I'm not sure what the link is between advertising purposes and having an IP address? Please explain that.