In the Classic Client, Cartography had but one practical application other than deciphering treasure maps. This use was in pinpointing the chest to dig it up. You could plot an X-course from corner to corner on the treasure map, get somewhere near it, and make a local map. You could then plot another X-course on the local map, and compare landmarks to get as close as possible to the chest. I really like the features of the Enhanced client, but when you plot a course on the map, it only lays down a pin, and doesn't connect them with lines, so you can't make that oh so helpful X. I have found that I have to switch to Classic Client to pinpoint a chest, and then switch back to dig it up and fight the spawn. I would like to see the connecting lines added back in to the Enhanced Client's Course Plotting feature.
Sure there are archives of treasure maps, but they are very incomplete (and often inaccurate), especially when it involves a map that isn't in Trammel or Felucca. Even these, however, are not completely accurate. There are several different archives with discrepancies in coordinates between them.