Although keeping your certificate of destruction is not essential, the document shows you are no longer responsible for the vehicle. Insurance companies may ask for a Certificate of Destruction to prove that your car is longer used and has been dealt with according to DVLA guidelines.
If required, most people will keep their COD to prove that the car is no longer their responsibility. However, sometimes, an insurer wants to see a certificate copy to confirm a damaged vehicle. You must forward the COD to them to satisfy your insurance coverage conditions.