Rest days are crucial in a workout routine as they allow the body to recover, repair, and adapt to the stresses placed on it during exercise. During rest periods, muscles recover from fatigue, and micro-tears heal, leading to strength gains over time. Adequate rest also helps prevent overtraining, which can result in injuries, burnout, and decreased performance. Incorporating rest days into a workout schedule promotes long-term fitness sustainability, ensuring that individuals can maintain consistent progress and overall well-being.