What effect do Walter Mitty's daydreams have on the story "The Secret Life of Walter Mitty?"

In James Thurber's entertaining short story "The Secret Life of Walter Mitty," the main character's daydreams remove him from the irritations of his mundane life by providing him with an heroic alternate reality. For example, at the beginning of the story, he imagines himself the pilot of a Navy plane that is about to enter a storm:

"The crew, bending to their various tasks in the huge, hurtling eight-engined Navy hydroplane, looked at each other...

In James Thurber's entertaining short story "The Secret Life of Walter Mitty," the main character's daydreams remove him from the irritations of his mundane life by providing him with an heroic alternate reality. For example, at the beginning of the story, he imagines himself the pilot of a Navy plane that is about to enter a storm:

"The crew, bending to their various tasks in the huge, hurtling eight-engined Navy hydroplane, looked at each other and grinned. 'The Old Man’ll get us through,' they said to one another. 'The Old Man ain’t afraid of Hell!'". . .

Walter Mitty is actually driving with his wife, who ends his reverie by telling him that he is driving too fast. After his wife reminds him to put on his gloves, he imagines that he is a surgeon: 

"A door opened down a long, cool corridor and Dr. Renshaw came out. He looked distraught and haggard. 'Hello, Mitty,' he said. 'We’re having the devil’s own time with McMillan, the millionaire banker and close personal friend of Roosevelt. Obstreosis of the ductal tract. Tertiary. Wish you’d take a look at him.' 'Glad to,' said Mitty."

In this incident, Mitty removes himself from the drab reality of his wife's reminder that he should put on his gloves by imagining that his gloves make him a respected doctor. His daydreams help him make up for the boring reality of his everyday life and for the way in which his relationship with his wife makes him feel less-than-powerful. His daydreams make the story more entertaining and lively, and they also allow the reader to understand a great deal about the way in which Mitty experiences his life.