There's a certain advantage to a kingdom in a fantasy novel where politics is not central to the plot. Your readers are familiar with the concept so that it doesn't distract from whatever is central. It still needs to be sketched in with enough detail to be convincing (with all the problems of research entailed), but it does not need the reader to concentrate on it and pick out all the details to figure out what sort of country the characters ramble through. Some superfluous details help as local color, but not too many.
Which, come to think of it, applies to many, many, many things that are used as backdrop. Sneaking through the kitchen with the cook roaring at the kitchen boys to move -- they're not characters as such, they are setting. A royal menagerie, thrown in just to show the king's power, can have dragons and gryphons -- and perhaps a yale, its horns swiveling about, but too many exotic to the reader creatures mean that the menagerie gains too much significance and draws too much attention.
Assuming, of course, that's not a hint that it is more significant and ought to come out of the backdrop. Writing's full of balancing acts, and determining what needs to be squelched as background and what needs to be developed as central is one of them.