Faerun has the Sea of Fallen Stars, the Shining Sea, and the Lake of Steam, all of which perform a similar function. They break up large land masses and provide lots of visual texture for the lands around them.
Krynn, although smaller, has its own New Sea that also breaks up what would otherwise be a fairly uninteresting large blob of land.
The Judge's Guild City-State campaign world is almost the inverse of this rule, as it is more centered on the water than the land, but ultimately the cartography serves the same function. The contours of the Barbarian Altanis and its surrounding lands just scream out for attention. We have the Trident Gulf and Sea of the Five Winds, and their associated waterways, to break up otherwise-boring land masses.
Given the history of the Mediterranean in the history of the world, one wonders if we would have seen any of the cultures of the Greeks, Egyptians, Romans, etc. evolve if they had not had access to its waters (which, in everything up to modern times, was a quicker and cheaper way to travel long distances than overland, with certain exceptions). And if you look at it from a cartographic point of view, it certainly divides Europe from Africa with intriguing contours.
Contrast these examples, then, with something like this:
Masterful storyteller and linguist though he may have been, no one claims Tolkien was an inspired cartographer. Middle Earth is, plainly, dull in terms of its geography. If the Brown Lands had been a sea or large inland freshwater lake, connected perhaps to the Sea of Rhun to the east, I think the map would have a lot more verve.
Speaking purely on an aesthetic level, what do you think contributes to a fantasy world map being interesting?