If you're at war with opponents who can field advanced military units at the beginning of a Dark Age, adopting Cyber Warfare will help you hold out until you can make peace with them. You'll want to replace it as soon as possible, though, because they'll have a stronger incentive to go to war with you again when their Grievances against you aren't decaying. This does not affect Warrior Monks.
The highly interconnected weapons systems of the information age rely on a mix of military and commercial components, processes, and software, creating what is essentially a new logistics reality for military professionals. Although interconnected weapons systems provide enhanced firepower and effectiveness (as anyone who’s witnessed highlight reels of smart bombs striking can attest), they do create a potential weakness. An opponent can attack the computer infrastructure of a modern military, often achieving better results than if they had tried to attack that same force directly. "Cyber Warfare" can roughly be defined as a formal attempt to degrade, destroy, or weaken the communications and computer infrastructure of a modern military. Some military theoreticians also use this term to refer to operations against civilian targets, like power grids.