I do not get too many comments on this site. But when I do, I sometimes keep them. If they are not an ad and are somewhat comprehensible and complimentary, I keep them.
But in order to prevent the spammers from getting any traffic, I edit the URL to point to my main page or the page that got the comment. I also remove the email address. Then I usually add some text indicating that the comments have been edited.
Image from Wikimedia, assumed allowed under public domain.