I've reevaluated the question and voted +1. I did it because of the following:
Some hosting providers have problem with bigger boards that have quite a lot of attachments because all of these attachments are in one folder only.
What makes difficulties for backuping or copying attachments via FTP.
But nevertheless I'm not completely sure that this implementation could solve the problem: if the board is very big might be that is not enough to simply subdivide attachments by years.
If a host has such limitation, today is not a good host or the hosting service is not properly configured: this makes that host not adapt to host big board in its servers. So mightbe it will be more useful to definitely change host and transfer the forum elsewhere.