Visuals on the map itself can help fuel a mental picture of the heroic tales the dice are telling, and make keeping track of environmental hazards and hurdles easier.
The battle map solves this, allowing the players to see themselves, visible enemies, and measure the distance in between themselves whilst waiting for their turn to come up.
If you play a more sandbox type of game, then this map can take on a more functional role as it will likely be divided into hexes, your greater exploration charted by which hex you wish to explore next. Sometimes this is just used for illustrative or reference purposes so your players can better grasp the world they vicariously live in and therefore plot their travels accordingly.