“God help you if you use voice-over in your work, my friends. God help you! That’s flaccid, sloppy writing. Any idiot can write voice-over narration to explain the thoughts of a character.” So says screenwriting guru Robert McKee (played by Brian Cox) in Adaptation.
I agree… almost.
If you’re just starting out, yes: avoid voice-over in all circumstances. You must first learn how to write an effective screenplay without V.O. before you can understand how to use it successfully. Film is a visual medium, and it’s the screenwriter’s job to show the story, not simply tell it through narration.
It would be unfair, however, to say V.O. is never a useful tool, but the beginning screenwriter is not skilled enough to know how to use it effectively, and the probability of forcing us through the story with unnecessary or jolting narration is high.
The skilled screenwriter, on the other hand, can craft wonders when executing V.O. properly. Consider William Holden’s cynical, beyond the grave narration in Sunset Boulevard, Morgan Freeman’s smooth and harmonious tone in The Shawshank Redemption, Robert De Niro’s increasingly disturbed mind in Taxi Driver, or Edward Norton’s razor-edge delivery in Fight Club. These films are great examples of exemplary voice-over use because the writers are careful not to describe what the audience already sees. Rookie mistake.
When using V.O., it’s paramount that you create layers and let the audience add it up.