"Piranah Lagoon" is the name of my Slickee Boys cover band!
When I found my way to BX many years ago, I was tickled that scrolls could be more than just extra or new spells. The two main twists were the protection scrolls and the maps. The idea that the rules included a mechanism for randomly dropping a plot hook into the party's collective lap was quite remarkable (to me).
Fully a quarter of all scrolls found are maps, according to the random table in Cook Expert, the book suggests the DM make up several maps ahead of time and have them handy to use as props for when/if the party finds one.
In the Basic rules, the description suggests that the map lead to a treasure somewhere within the same dungeon, but the Expert rules rightly expands it to include possible wilderness travel. The tables results scale for the size of the treasure to be found, as well as having magical items as loot. There are also suggestions for placing monsters as guardians.
Two things occur to me off the bat: Firstly, a treasure map is a great way to delay a party from getting hold of too much wealth at once. Of course the loot from the dungeon isn't light! You just haven't gone to the haunted tower on that map to retrieve the fabled Emerald of Kun Par yet! This can be especially useful if you need a little extra time to figure out some things in the game.
Secondly, it's a great segue into the next adventure that saves you trying to get the players hooked. They know where a fabulous magical item (or pile of cash) is supposed to be, they just need to get their collective butts in gear and start walking.
Of course, they could try selling the map (for a fraction of the loot's value). But that could lead to even more plot hooks and complications. In a fun way!