I like having more than one, mostly for the reason Del gave. Once you get to the point where you've discovered everything there is to discover on a world map, that takes a lot of the excitement out of the game, so finding out that you have a lot more of the game to go is an awesome feeling. At least if it's a game that's worth playing. FFV's use of
(SPOILER)two world maps that eventually merged to form a third was awesome and one of the best uses of world maps in the series. Wish more RPGs did things like that.
Mirage also nailed the way a good JRPG should unfold, which is the main reason I like games like FFIV through VII a lot more than games like FFX, where the progression was almost entirely linear until you got to the end of the game. In FFVI, for example, once you get the airship the WoB allows you to do a lot of cool sidequests, and that's only about a quarter of the way through the game. The WoR is even more non-linear.
Of course, none of these can compare to the sheer ingeniousness of the world design of something like
Super Metroid, but the early FF games and the
Chrono series did a pretty good job regardless.