Hey, this idea isn't stupid. The attachments are not organized in any way.
I think what he means is the following:
Board UBB1
Board UBB2
Board UBB3
/attachments/UBB1 ; announcement board
/attachments/UBB2 ; files for users
/attachments/UBB3 ; avatars
He has different categories and wants sub directories so that he can directly see which files are belonging to which category. I think that give a nice overview how much space a category needs and could initialize a cleanup (delete old shite

))
Nice suggestion I think but I see also problems. What happens if a thread with an attachment is move from one board to another? Also the attachment must be move then etc...