Steps to Reproduce
1. Upload a document
2. Check out your /document_library/10132 directory, you'll see it created a folder with the document reference - this is normal.
3. Create 3 Users
4. Go to Control Panel -> Server Administration - Click on Reindex
5. Go back to the /document_library/10132 directory, you'll see now that there are several empty folders that have been created.
These folders correspond to the GroupID in the Group_ table - basically, Liferay will create a folder for every entry in the Group_ table.
(see 3 attached screenshots)
While this may not seem so malicious, for Liferay implentations with 32,000+ users on a Linux EXT3 environment, this is a big problem.
The Linux EXT3 system has a hard limit of 32,000 subfolders (http://serverfault.com/questions/87054/mkdir-cannot-create-directory-foldername-too-many-links), and if Liferay creates an empty folder for every user, then it will reach the EXT3 cap and you will be unable to upload documents in Liferay, even if in reality, you have only a few documents in Liferay.