So say you've got a custom warning of "Bad words in Forum C", if a user racks up the appropriate amount of points that triggers the Warning Action then it would only count the points for that specific warning type. This would allow you to ban someone from a specific area of your forum based on action in that forum. Hope this makes sense.
You could have different triggers for different Warning Actions i.e.
10 points "unspecified" = A specific Warning Action
5 points "Bad words in Forum C" = Another separate Warning Action