II_UUID_MAC, when set to TRUE, uses an older algorithm for generating UUIDs on Windows.

For security reasons, the uuid_create function on Windows no longer uses a machine's MAC address to generate UUIDs. You can use the II_UUID_MAC environment variable if you do not need the level of security provided by the new uuid_create algorithm and for the sake of compatibility want to continue to use the MAC address of your machine when creating UUIDs.