It can be enjoyable to engage in a spot of ye olde world-building, and the preparatory work for stories is something I quite like doing.
However, there’s a potential pitfall, which is known as ‘info-dumping’. Basically, info-dumping is when, instead of weaving elements of the world or plot into the narrative it gets dumped all over the reader in a massive block of text.
This can take the form of a dialogue where things the author wants to convey can be clunkily thrust into the face of the reader. For example, imagine a city where drunkenness is rife (I know, I know, this is hard for an Englishman to imagine. But try). Instead of having two chaps exchanging statistics on liver disease and tutting noisily, it’s more natural (and more enjoyable to read) for them to be stepping over a rancid snoring drunkard lying in a pool of his own vomit whilst they walk along a raucous street full of taverns.
It can break immersion or just bore the reader when there’s a ream of information that’s presented in a clunky or tedious way, especially if it’s not relevant to the plot or protagonist.
Guy Gavriel Kay did a very good job with Tigana, when there was a lot of exposition regarding the backgrounds of characters. The reason it worked was because it was relevant, it informed the reader about the motivations and suffering the characters had undergone and enabled us to understand them better.
Another related problem is when describing something becomes excessive in its detail. The difficulty is that some people love tons and tons of precise detail and others like a fairly hazy picture, wanting the author to give them the gist and allowing their imagination to flesh out the details. There’s no right answer, although subgenres do differ slightly. An epic fantasy might have more detail than a rollicking yarn (A Song of Ice and Fire and Tales of the Ketty Jay, for example). Detail and Pace are like two kids on a see-saw. When one’s high, the other should be low.