Military: Maintain tactical level classified information and the secrecy of planned tactical operations (Midian's TVS-2 and VS-1200).
Police: Keep criminals & news media from listening in on police communications. Criminals that eavesdrop may use the knowledge of police communications to avoid detection by police & plot activities. Protect sensitive information from being used by the news media or crime scenes from being interfered with prior to a police arrival.
Ambulance: Secure communications maintain the integrity of patients' information (HIPAA) from being intercepted when transmitted over the air.
Fleets: Taxi, towing and fishing competitors often use information intercepted over the air to take business from one another.
Industry: Some extreme activists eavesdrop on chemical and mining companies' communications. These activities can cause unnecessary harassment and litigation and may cost the companies financially.
Utilities: In an effort to protect a country's infrastructure, utilities are encrypting communications to prevent outsiders from learning information that could expose weaknesses in construction, operations, etc. that could make the site a more susceptible target.