Of course, there aren't any rules in writing. But when something is used in exaggeration (or even Isn't used at all!) without prudence, it can ruins everything.
A voice is like a guide to see the story and/or the world as he views it through his opinions, points of view and vocabulary, like feeling and knowing something new. But it can also be a neutral one that allows the reader to understand the story with his own vision, like flying free.
From neutral voices to opinative ones, how to use them in moderation and how do we know we are using them too much or too little?
The "neutral narrator" can make the story sound boring. Just like as an eye that looks but don't see. An ear that litsens but don't hear. So instead of flying somehwere, you dont fly to anywhere.
This can be a real problem if you are trying, for example, make some comedy book and your narrator is cold and neutral. Imagine if Douglas Adam's Hitchiker's Guide narrator were a neutral one? All his jokes about the vogons and many other things could be ruined!
The so-called "intruder narrator" can make the story sound like a moral lesson or a dogma being teached. It can point out to a truth that is absurd and strange for the reader. Rather than learning something cool, you learn something "cool" you learn something that "burns" more than a volcano!
I guess I dont even need to give examples of that one. You want read a fantasy book and the guy writes some political book with many moral lessons.
PS: I would also like to remember a thing about that: the narrator's voice isn't necessarily the writer's voice.