can you just explain in simple way.

 Yes, I do think it makes the story more interesting. By shifting back and forth between the different stories, Thurber shifts between two levels of reality. In one, we get what is actually happening, while in the other, we get what Walter is daydreaming about. However, Thurber makes the daydream as vivid and credible as the reality, and so it is clear that the daydream is very important to Walter. It's how he makes it through the day.