The purpose of a black list is to save the moderators' time and resources.
If a particular account is being used to submit a high volume of off-
charter posts, this permits the moderation software to return the articles

Contrary to minority opinion, this is not censorship.  The unmoderated
newsgroup is still sitting right next to
RSPWM, and since the post was returned to the author they can still
post it where everyone who can read RSPWM can still see it.  It's
just that those readers can also ignore it that much more easily if they
so chose.

The only account currently in the blacklist is

who has submitted over a dozen copies of his web page ad.  He does not
reply to emails, and his provider has not yet taken any action.