FTP sub accounts are the simplest way to authorize your friends and colleagues to work with the files within your account. Each FTP user of a Linux hosting account can be given a separate username and password, which gives full FTP permissions to a single directory, without giving access to the parent directories, or the control panel. No dedicated IP is required for FTP sub accounts. Each FTP sub account has a login which is different from yours. For Windows accounts you can also have several FTP user accounts, however, you cannot restrict access to certain directories.
Virtual FTP provides more possibilities than FTP sub-accounts. You can give your authorized Virtual FTP users access to more than one directory and specify a different set of permissions for each directory. Virtual FTP users log right into your root, but can enter only those directories you allow them to enter.