From the top part of the System Variables help documentation page:
Furthermore, you can also use the
%USER%,%HOME%,%USER_FULL_NAME%, and%DOMAIN_HOME%variables. For more information about these variables, see "Directory Access Rules"
In general, it's best to use the $ macros for events and within system messages (like login messages or customized FTP responses) while using the % macros for configuration values. Many of the $ macros don't have explicit values are until a session has been successfully established or a specific action has taken place (like a file transfer) whereas the % macros have explicit values at all times.