Reference: Advanced FTP Server Options
This option tells the ftp client interface to perform all actions relative to the default path associated with the user account. It must be checked when an ftp server (such as an IBM MVS system or an AS400 system) is unable to process combined file and path information. All directory and file operations are performed separately. It is not possible to access any directories or files outside of the starting path specified for the account. Typically, servers that require relative addressing will also need an FTP Server Type defined.