It's not utterly useless. You can use that to get coordinates for any address and then store that info in your database. Coordinates can be used within the Pro Maps wizard instead of the address string.
Anywhere in the wagmp_map_1.php file that calls "geocoder.getLatLng" is grabbing the coordinates from the google maps API. Once the coordinates are returned, it attempts to cache that info in the XML file for later use. In the past, any issues I've seen with the cache file have been permissions related. All it is doing it trying to open the file and write a new entry. Then later it reads that file and uses the cached values if they exist.