> Stefan told me that the change was because some users were having thousands of yymmdda.log files
> in the logbook directories, and that sorting them into subdirectories by year at least did something to bring some 
> order.  Possibly to get around the lazy archivers, I suspect.

I'm actually the culprit, who did ask for it.

If you want to know the full story, here it is:
We have our logbook data of our accelerator operation logbooks on AFS (Andrew File System). 
And apparently AFS has a bloody stupid, hard coded limit: 
the total length of all file names in one directory cannot exceed 64k.
Our operation logbooks go back for more than a decade and do contain many, many, many attachment files.
One day - very unexpectedly - we did hit that limit. 
Removing temporary files (generated picture thumbnails) bought us time, and Stefan was nice enough to upgrade ELOG swiftly for us: a big "Thank You" to Stefan!