FAQ

We can't be sure, it's pretty much left up to the viewer to decide, which is probably intentional on the part of director Terry Gilliam. Gilliam almost always invokes an element of ambiguity in his films. It can be likened to Total Recall(1990), The Wizard Of Oz, or K-Pax

He might have wanted them all alive to get more info on how to use the map. Evil's very intelligent, seemingly all-knowing like the Supreme Being but he may not know everything, including how the map works. If he keeps the dwarves alive, he can probably torture them for info on where the time holes are and which might be the best to exploit.

Also, if he had, the movie would've ended right there -- the dwarves might not escape and mount the counterattack they did.

The map belongs to the Supreme Being and is a guide to all the holes left behind in the creation of the Universe, which constitute inter-dimensional portals to various points in history. As Randall explains to Kevin when they arrive in Robin Hood's time, they were the Supreme Being's assistants, who helped create, at least, the world of humans, IE, Earth. When they weren't compensated/paid properly for all the work they did, they bitterly stole the map with the intention of robbing the richest people and eras of history.

Evil himself, also slighted by the Supreme Being, wants the map for basically the same purpose the dwarves have -- plundering the world for it's treasures, though Evil seems more interested in stealing technology for his own gains. He also seems to believe that it is or may be a stepping stone to seize control of the Universe from the Supreme Being.