By sharing machine-readable records, libraries can readily learn what maps other libraries have. Preparing lists and bibliographies. This is much easier to do if the maps are cataloged. Circulation and inventory control. Digging through a pile of maps to find what you need is very hard on them.
Uncataloged materials are a waste of staff time, too.
Reference questions take much longer to answer when the maps are uncataloged. A second edition is in the works. Map Cataloging Manual. NOW, while the collection is small enough to make it easy to do. Store unfolded any map that you wish to have around for a long time.