It tells them quickly what they want to know. It also serves the reporter by forcing her to sharpen her news judgment, to identify and rank the most important elements of the story. But the inverted pyramid has big disadvantages. Although it delivers the most important news first, it does not encourage good writing. There is no suspense.
Reporters tend to lose interest, time and energy.
Writing in the second half of the story is casual at best, and poor at worst. One alternative to the inverted pyramid is narration or story telling. Narration uses scenes, anecdotes and dialogue to build to a climax. People are prominent in the story, and they are responsible for the action. The story has a beginning, middle and end.