Rest days in a workout regimen are important for muscle recovery and overall performance. During exercise, muscles experience micro-tears, and rest days allow them to repair and grow stronger. Insufficient rest can lead to fatigue, decreased performance, and an increased risk of injury. Furthermore, rest days help replenish energy stores and reduce mental burnout, making it essential for maintaining motivation and consistency. Active recovery, involving light activities, can also aid recovery and maintain fitness levels without straining muscles.