People think the best part of the story is the climax. While that should be the place where everything culminates, it is in the calmer scenes leading up to this that the energy is built. If every scene was as exciting as that one, then the audience would be exhausted far before reaching it.
Quieter moments are great times for characterization. You learn about the people you are dealing with, what their thoughts and feelings are, and the wheels start turning. A tale takes time to build up speed, but once it does, it is like a freight train barreling through the night.
The shorter the story, the briefer these interludes will be. A longer work is more conducive to deeper characters, so there is a great deal of calm before the storm. And just like the interval between the thunder and lightning, these moments when properly spaced can steadily build the excitement to a fever pitch.
These are also good opportunities to subtly advance the plot. A myriad of things can creep about unnoticed until they are ready to strike. And when they do, there will be more impact, due to the element of surprise.
Works tend to be predictable when everything is loud and all the scenes are big. However, a reader will take on an expression of shock, if they realize that the monster has been sneaking up behind them the whole time. Or they find the plot which seemed so clear was just a diversion and the story takes unexpected twists and turns that have them clutching the arms of their chair to keep from falling out.
That is when the terror is greatest and the drama most intense. The reader has no idea where you are taking them, but the enticement is just too great to stop. They must know what happens next. They must reach the ending, bewildered though they may be. For after the calm, one experiences the true fury of the tempest.