It provides a Reserve of aircraft that can mobilized and as a huge source of spare parts.
A recent example.....the USMC brought back into service some CH-53D's to make up for some shortfall and were able to do so in a fairly short time.
DM is also the source for F-4's for use as Target Drones.
Plus......a lot of Soda Pop cans are made from the scrapped airframes!