One of my enduring loves and probably the thing that originally drew me to role playing in general and GMing in particular is world building. When I was younger I did a lot of writing. Well... I told myself I was writing, in reality I was doing a Tolkienesque thing where I was just using the writing as an excuse to construct races/languages/maps/characters and places. Since starting roleplaying around 18 months ago, I've found that I still love it especially as expressed through maps. I'm not talking about the small floorplans that litter many published rpg books, these have their place but I find that often they are too sparse to inspire anything more than a drawing on a grid to position minis. There is something about a BIG, well depicted and detailed map that I love and just makes me want to study it for hours. From where I'm sitting in my room at the moment I can see a map of Lovecraft's Dreamlands for CoC, a map of Ansalon from the Dragonlance setting and a map of Eberron. And that's just the ones that are pinned on the walls! One of my favourite recent purchases was Tasslehoff's Map Pouch, which was where the aforementioned map of Ansalon came from.
How often do maps make it into my games though? Well, I've been lucky with my current campaign as Call of Cthulhu is one of the most well-supported RPGs props-wise both from official sources and the fanbase. As such, every major location my group has visited across the real world (Arkham and Kingsport) and the Dreamlands (Ulthar, Hlanith and Celephais) have been accompanied by small (A5 or so) maps detailing the major locations, organisation and so forth. There is a player in my group with as much of a fascination for the intricacies of the world as me and more than once the other players have had to break up a discussion on the architecture of the palace at Celephais. But in the past, and certainly with other systems I have not been so lucky, which is a vast shame because I think maps can add a whole new level of immersion to a world. They can also help to match up the way everyone's perceiving the area rather than just having a few abstract points of interest and jumping between them without any detail of the route or what they're likely to encounter.
That said, I think my enthusiasm for getting maps into games is probably misplaced. Floorplans and area maps are useful mechanically, they set up ranges and keep everything uniform and calculable. Larger maps are less useful in this respect especially when travel times are so elastic that the distances are usually not a huge problem. Whenever I have introduced a larger scale map to the game, the players have skimmed it and then pushed it to one side unless they are looking for a particular location. Therefore I think that maps are a nice tool for GMs and certainly nice to look at, but attempting to bring them to table as an actively usable prob is probably doomed to failure. The scale is too large, there is too much detail. Even in an investigative game like CoC, odds are high players don't want to be presented with a huge list of cities they need to research and decide which they want to go to next, and if they know where they're going then the map is largely redundant even if the world building suffers a bit.
I will finish on a positive note by saying I have had a good experience with a big map when the players in my Dreamlands campaign secured a boat and needed to plot a voyage (I won't say to where so as to spoiler nothing). They spent a good time looking up cities in their 'Rough Guide' and plotting a course, complete with rest stops and sight-seeing. A good time was had by all and I got to show just how deep the rabbit hole of world detail goes with the interesting titbits and legends they found.