This variable allows disabling the nofollow feature in Vine Type. Sorry for all the negatives in that statement; I'll try to say it in a more positive manner.
Vine Type, by default -- even when
$comment_nofollow does not appear in your vinetype.config file -- discourages manually-entered comment spam. It does so by placing "additional information" into comment links (visible to Google and other search engines but invisible to the internet visitor) that marks the link as not endorsed by the site's owner -- that's you.
By placing this additional information, called a nofollow attribute, comment spammers, whose only goal is getting Google to notice their sites, are discouraged knowing that their links are specifically marked as untrustworthy.
So by default, nofollow is on.
This variable, however, allows you to turn off that feature. To disable the nofollow feature, specify