When you open the cover to a fantasy novel, more often than not you find a map of some sort. Perhaps it is just a less-than-detailed drawing, or maybe it is a full-blown map that stretches over two pages and is packed full of information. But the question is - is this information actually helpful?
In the Christian fantasy series The Binding of the Blade (by L. B. Graham), there was a map just before the beginning of the prologue. Not too detailed, but perfectly sufficient for what the reader needs. It outlined all of the major cities--and the towns that were important to the plot--as well as mountains, rivers, plains, etc. I used it quite a bit to keep the cities and places straight in my mind.
Now, there are also other books that I have read where I barely glance at the map at the beginning. They're either not too detailed, or I just don't need to use them.
So what's the difference? Why do I use one map and not the other? Why are some maps helpful and some not? I think it depends on three things.
First, the number of places, cities, forests, etc. determines whether or not a reader uses a map. If a novel stretches over as much ground as The Lord of the Rings, for instance, the author needs to have a map. Otherwise, the readers will find themselves bewildered and lost in the names and places. But the opposite is true as well. The author could make the protagonist tramp around in only one town for an entire novel--in which case, a map is not needed.
Second, the names matter--albeit to a lesser extent--in deciding whether or not a map is helpful. In The Binding of the Blade, the names all sounded a little alike, enough that I checked up on the map to match the name to the place. But places that have names like 'Bobton' and 'Littletown' aren't that hard to keep track of, especially if they are small in number.
Third, it depends on the reader. Some readers have great memories--some, not so much. Some people use maps often, and others barely glance at them.
Since fantasy novels often tramp over large areas, and those areas often have strange names, it is my opinion that fantasy maps are helpful--depending on the reader.