If this variable is set to True, the WBSP engine will allow owner of the site (author, user that creates WBSP files and uploads them to server) to use absolute path names, i.e. to access files outside his wwwroot directory, files located on other disks or even other network computers.
Setting this value to True can have great advantages on intranet (or if you use entire server exclusively) but it is not wise to set this to True on shared web server with many users. Default value is False.