As with the ability to move our narrative focus anywhere there are benefits and risks to omniscient narration when it comes to explanation. The narrator knows and sees all so it can be tempting to thoroughly explain everything, even when we don’t need to. This can be useful in a first draft when we’re figuring everything out but it can be cumbersome and slow the story too much. This isn’t to say that all explanation is bad, in many ways there are advantages. For example, in first-person/subjective narration we’re limited to the knowledge of, usually, one character so there may be things a reader would like to know but the character couldn’t believably answer. An example might be if a magical character is working a spell, a narrator character might have no idea what they’re doing but an omniscient narrator would. We might argue that a narrator character learning how something works can be an interesting story but that isn’t always the story we want to tell; if it isn’t the story we want to tell in first-person than the reader might never get the answer.
On the other hand because we have the ability to put all this knowledge on the page it might be tempting to put too much exposition on the page, a cliché might be thorough descriptions of technology or weaponry that don’t add anything to the story. In a sci-fi story it might be interesting to know how a futuristic weapon works but do we need the same information for weaponry we see in modern day films? Once again, it would depend on the story involved but it is something to consider. It might be important to note that in this instance I’m applying this question to the narrator not the characters conversation. Information about a character’s weapon of choice might be cumbersome in the narration but that doesn’t mean they might not tell a person about it.
The primary problem with the risk of the narrator telling too much isn’t simply the flow of the story, though this is very important, but also what the reader needs to know. As with our discussion on showing events that might take away the impact of future reveals the same is true of exposition. My example was the reveal of Darth Vader as Luke Skywalker’s father. We could’ve seen this or we could’ve had a character tell us, either way the impact is the same because the audience having the information before the big reveal takes away the impact of the reveal because it isn’t new and unknown.
It can be difficult in omniscient narration to find a balance because we don’t have a limitation on the narrator’s knowledge, sometimes we simply have to write and then cut or add later on to find this balance. A good question to ask is often, ‘does the reader need to know this right now?’ If not it’s often fine to cut the information and spread it around the story.