First of all, there is no consistent concept of what a hidden file is and and how hidden files are distinguished from normal non-hidden files. Microsoft Windows (using FAT or NTFS) for example has a special file attribute which marks a file as being hidden. On Unix however, there is no such attribute and files starting with a dot (dot-files) are considered to be hidden.
There is no specification about what an FTP server should return if a user requests a directory listing which contains hidden files. Some servers show them, others don't. (The latter are considered to be broken.)
If an FTP server is hiding files from the user but the user wishes to view the hidden files, FileZilla offers the option to try to list the hidden files if Server->View hidden files is enabled. However, there is no guarantee that the server respects this non-standard command.
In some cases, a user might not want to see all files in a given directory but only files which match a given criteria, for example only files ending with .txt or files starting with TODO.
In order to satisfy such needs as well, FileZilla has a powerful filter facility built in: Edit->Filename filters....
Note: Keep in mind that even if FileZilla is filtering files from the file list, the complete list still has to be fetched from the server as filtering takes place at the client and not at the server.