This is an exercise that is necessary to practice in case you find your heli in a compromising situation. These situations are not always based on pilot error either. As we all know, the electronics can experience some type of glitch, or the battery may puff up and fail. I haven’t had to perform one in a real life situation, but I have had many successful auto-rotations on the sim. An auto- rotation is a practice where, when the heli is in flight, you cut the throttle while maneuvering the heli to the ground safely and with a bit of timing you flare the blades thereby allowing the heli to lift and gently land. With consistent practice, this is a skill you will dominate and be glad you did. It is a skill you can consider as a form of insurance for your investment.
Here is a great example of an auto-rotation performed successfully with a compromising situation.
Here is an example of auto-rotations in practice.