In all writing, we need to have a willingness to let go. This has two meanings, in respect to the written word, I think.
First, there is letting go in the sense of letting the mind go, letting the conscious mind get out of the way. This is what Isaac Asimov talked about in his article on the Eureka Phenomenon in The Magazine of Fantasy and Science Fiction (June 1971; reprinted in The Left Hand of the Electron). It is the state of dealing with writers block, or thorny scientific issues, by setting them aside, letting them go, in order to do something mindless – take a walk, watch a mindless action movie, do dishes, whatever. The idea being to keep the conscious mind occupied while the subconscious works out the solution.
Second, there is letting go of elements of a given work. This applies, I think, equally well in writing (fiction or non-fiction) and worldbuilding. For writing in general, this letting go is why it is often better to err on the side of being short in drafts rather than long. There is always room to add more detail, more evidence, etc. On the other hand, it is always more difficult to cut material.
In fiction, letting go could mean removing a scene, dialogue, or even a character that is just not working. The element could be simply taking up space without helping the plot or it just might not fit. Perhaps it is even a great scene or character, but just not right for this story.
With non-fiction, the point of letting go could be the claim, quote, or even thesis that just doesn’t add anything to the argument, fit with the rest of the claims, or seems shoehorned in to get one more piece of evidence regardless of usefulness. This is the cause of the 24 minute presentation for the 20 minute conference session that needs two pages cut, but the presenter keeps trying to whittle away a bit more up to the last minute before presenting. Every scholar has seen this, I’m sure, at one conference or another.
In worldbuilding, letting go could mean cutting that place, culture, society, or other element that isn’t fitting in. That could be the city, organization, or species that gets pounded into place or just doesn’t flow with the rest of the world in some way, or which seemed like a good idea in the early stages, but never got developed. The last may sit there taking up empty space, both in a “worldbook” and on the map. Sometimes, those elements just need to be dropped entirely or put to the side for a different project in the future.
A consequence of not letting go is a very busy, overly packed fictional world or a discombobulated paper, book, or story. As the old adage goes, sometimes, less is indeed more. Pruning, like any form of editing, should ultimately produce a stronger final result.