Here I have the map of my explored area so far. My house is that brown 2x1 thing a little south of my position. My farms are the various green and brown areas below that. I haven't done much in the way of buildings, basically my house and my farms and a few tiny mines that don't even show up there.
Here we can see my home "The Sand Sea", the area south is the "Black Forest" below that is "Bogwood Marsh" above is "The smiley islands" to the east is "The Icy Plain" and below that is "The regular plain" in the northwest is "The hilly forest place" and the southwest is "Holycrap Mountains"
Maps are good when you go on large expeditions. Instead of having to rely solely on a direction (aka compass) you can see where exactly you are. This is most useful when you make the map at your home, setting the center to be your home base.
I've also used a map to find fortresses in the Nether. Instead of having to memorize every place I've been, or placing "breadcrumbs" to find my way back, I can simply look at the map.