This is an option disabled by the default UI. It is a minimap that appears on the screen showing the current map, the position of your character and the party/raid members. In battlegrounds, it shows even the bases, in Arathi Basin it will show all the five spots, stable, mine, lumber mill, blacksmith and farm.
How to activate the minimap?
Open the World Map or press “M”, at Zone Map select “Always Show”. Close the window.
Now you should be able to see the minimap on your screen. It can be configured: moved anywhere, tweak the opacity (0% will show just the characters).
Is it worth using it?
For example in Tol Barad, it can show all the raid’s members distribution without having to open everytime the default map. The same in battlegrounds.
It sometimes can be annoying as it is another thing that covers the screen. On big monitors this should not be a problem.