I like that. If it's not interesting, it's not worth telling.
Sometimes, even if it is interesting, it's not worth telling, because it's not part of the story being told.
I had a friend once who was known for spouting out non sequiturs. They were often very interesting bits of information, such as some obscure piece of history or some odd world fact, but they had nothing to do with the conversation going on (except in his mind).
For instance, we might be talking about a war in the Middle East, and he would make some sudden comment about Japanese cuisine. If you asked him, he could lead you through a long, convoluted path of how one thing led him to another, but it always came across as having nothing to do with anything, and it was somewhat annoying if you were in the middle of a good conversation.
While it's usually not nearly so extreme, fantasy and science fiction authors fall into a similar trap somewhat often. A typical author might give the whole story of how some ancient beast was brought down and the city of New Crobuzon was built in its decaying guts, and might even give the ancient tale of how this beast and another beast battled and all that.
But really, what would that have brought to
Perdido Street Station? Nothing much, I think. While there are some very interesting bits in PSS and Mieville's other stories that are tangential to the plot, they are usually just hints at larger stories rather than fully given stories in themselves. It tells you that there is a much wider world out there without giving you the details of it, and I like that.