The map is useless, Kabal gives it to you so that you can hide it in the Chaos ruins after you finish Konquest, after that you just get some Koins.

It's not useless, just annoying.
After you beat konquest, you can go back into chaosrealm and hide it through the light blue portal, thus allowing you to go back to Kabal and fight him to get his alt. costume.
ALSO, after you hide it, if you come back to chaosrealm later, you'll find Mokap near the light blue portal, looking for a way to get back home to Earthrealm, and you have to teleport back to the ruins to retrieve the map for him, and he'll give you yet more koins.
So yeah, you can't do crap with it til after you beat konquest, but you need to finish the quest to get Kabal's alt. outfit, and activate the Mokap quest, if you'd like to talk to Mokap that is. (He says bub alot. And not in a cool way like Wolverine.)