Emphasis:
* To highlight a key idea or concept: "He was not just tired, he was *tired*. He was exhausted."
* To create a sense of urgency or intensity: "We must act now, *now*, before it's too late."
* To draw attention to a contrast: "This is not a game, it's a *war*."
Rhythm and Flow:
* To create a sense of rhythm or cadence: "The *rain* fell, the *rain* poured, the *rain* drowned the world."
* To emphasize a specific part of the sentence: "He went to the *store*, to the *store* he went, and bought a *loaf of bread*."
Clarity:
* To avoid ambiguity: "I saw the *dog* that the *dog* chased."
* To reinforce a definition or explanation: "The word *love* can mean many things. *Love* can be romantic, *love* can be familial, *love* can be platonic."
However, avoid repeating words if:
* The repetition is unnecessary and adds no emphasis or clarity: "The *cat* is a *cat*, it's a *feline*."
* The repetition becomes monotonous or jarring: "The *dog* barked, the *dog* wagged its *tail*, the *dog* ran around the *yard*, the *dog*..."
* The repetition creates a sense of redundancy: "He *went* to the *store* to buy *milk*. He *went* to the *store* to buy *milk*. He *went* to the *store* to buy *milk*."
Ultimately, the effectiveness of repetition depends on the context and the desired effect. Use it sparingly and strategically for maximum impact.