XAID has the same effect as inserting an EXEC SQL SET CONNECTION statement before every EXEC SQL statement in a program.
XAID is mandatory when using more than one XAR defined with the same RM switch module type for use in CICS or Web Services applications.
XAID is mandatory when compiling the DB2 or Oracle SQL RM switch modules for dynamic registration that are also configured to run with User Impersonation.
See RM Switch Module Registration and the UserP=(T|F) section in SQL xa_open string Configuration Options for more information.