What is the disadvantage of not claiming a "Diminished Value" of a new car - 2016 involved in an MVA not your fault?

The disadvantage to not seeking to recover diminished value of a car damaged by another's negligent conduct is that you will not be fully compensated for your loss.    I assume that the insurance company has paid the cost of repairs, and possibly for loss of use of your vehicle during the time that it was out of service.    Diminished value represents the amount of money by which the vehicle's residual value was reduced as a result of being wrecked. Any car dealer will tell you that a car that has been wrecked, even if fully restored, is worth less money than a vehicle of like kind that has never been damaged.    I hope this helps.