No, that means don't ban. Originally l4d_ff_ban didn't exist because there was only 1 limit, so this was the old way of telling it not to ban.
I could have made it a perm ban, but if a server had the FF settings too tight they would accidentally ban players for too long. Instead, I recommend banning for a few hours. If it was an accident, then no big deal. If it was on purpose, then the player would either learn their lesson or get banned again.
With this plugin it is very hard for a player to ruin the game. I would recommend smaller limits with a short ban duration, instead of high limits with a permanent ban. With higher settings you will have less accidental bans, but a griefer would achieve his goal and the game would be ruined.
If enough people wanted it I could allow perm bans. But I think a better solution would be to store a timestamp with the player's steamid, and only perm ban repeat offenders within X days.