The full map: the usual reason people install this
Every Monolith echo is generated anew. Half the run goes on working out where to go at all: the objective can sit in a far corner or two steps away, and there is no way to know in advance. With the map revealed the route is visible immediately.
On a single run that looks like a minute or two. Across a hundred echoes in a season it adds up to hours, which is why the demand for map reveal holds steady even among people who want nothing else.
Dungeons work the same way, especially the ones where you circle around looking for the right door while a timer or a reward depends on how fast you get through.


