You can choose to organize the contents of a folder into automatically created subfolders. This can improve your site's performance, and ensure that folder listings are compatible with the 100,000 item limitations for syncs, FTP, SFTP, and WebDAV.

You can choose the Subfolder name type which determines how the subfolders are created. File extension will create separate folders for each extension found in the folder. Created date will use the date the file was added into your Files.com site. Modified date will use the most recent change date of your file (your site administrator can configure how the modified date is calculated). Regular expression accepts your own custom regular expression to determine what subfolders are automatically created.

When you configure a folder to automatically organize its contents into subfolders, you can also choose to Organize existing files if you have items in the folder already.

Refer to the Organizing Files documentation for more details on this.