Uploads through the admin interface go into the uploads folder with the structure year/month. This is usually fine, but what if I want to upload lots of past content? If I upload a lot of past content now, it’ll all end up in the 2011/03 folder, regardless of when the content was produced. This will be messy. The better solution is to upload each to its own year/month folder, a much neater solution.
However, manually placing the files into the desired folder structure does not cause them to show up in the admin interface. It turns out that WordPress doesn’t check the folders to see if anything is inside. A database entry is needed. This can be accomplished with the Add from Server plugin, which scans the directories and adds the required database entry.
This allows the files on the server to be added to the database and hence show up in the media library. The file will attach itself to the post which is currently being written, unless the checkbox “Do not add to current post gallery” is selected.