Even if it is not very common to locate industrial activity underground, on some occasion’s strategic or hazardous activities are carried out underground.
One example might be the manufacture of military weapons and machinery in times of war, which is carried out under the surface to avoid attacks from the enemy.
For instance, during the WWII , the Germans used worked-out mines to relocate some of their military industries because of intense allied bombing.
Another use of the underground space could be the storage of important computer servers, bank reserves, precious materials, etc.