As much as a camera that jerks back and forth between two disparate pictures can confuse the viewer, so can narration. But the narrator can do one thing a camera can't do, go into someone's head. We can actually describe someone's thought processes and emotions. We can explain highly complex concepts. We can write about things that the special effects department can't simulate.
Timing is everything.
As much as the delivery of a joke's punchline, a karate kick, or a home run swing of a baseball bat requires perfect timing, so does the release of information in a story. Too much information released at once creates dead space, the dreaded info dump. Too little information lessons your story's impact, like a batter that doesn't setup right for the proper follow through. Just the right timing and technique can give you a home run. I define Foreshadowing as showing the reader some information earlier in the story that is vital later on.