At least, according to this article:
Because the cicada killer wasp hunts and kills mostly cicada insects as a food source for their larvae they help to keep the cicada population down. Cicadas are a pest insect, they eat the deciduous leaves of fruit trees and can ravage valuable farm crops. The cicada killer wasp is a beneficial insect and is part of nature’s way to help maintain a useful balance of cicadas in the wild. They could possibly be the only bee that 'if you leave them alone they will leave you alone.' That's pretty good advice.