MetaMap adds features to the WoW world map, keeping all mapping type features in a single place. Some key features include the ability to adjust the map window size, move the map anywhere on the screen and adjust the opacity of the window & maps.
You can also save sets for toggling between 2 map modes and it also allows full player movement, messaging, etc. with the map open.
It also offers the option to add coords to the main map and the minimap and also add instance maps which open to the correct instance you enter. Plus much, much more.