I think It might just remove the 'Reason' box if no reason is given for a ban when the banned user is viewing the Banned Message...
...Or somethign along those lines. If so then I suppose its useful because people do get annoyed when you dont give them a reason and there is not always a simple reason and you might jsut want to get rid of them because of them being an annoyance.
I think some sort of Default banned message would be good though saying to email the Support for help or whatever if you cannot be bothered to type a reason. You could also have an option to show no reason - I have not got a clue how to do any of this but its an idea!