As an employee of a law enforcement agency, I would have to say that plain english is ideal for most instances. Fighting crime is a multi-agency effort, and there are many instances that the city police department, county sheriff's office and state police could get into a chase or other situation that could involve all agencies involved communicating via radio. If each agency uses different codes for different crimes/directions/descriptions/etc, it will be difficult for them to communicate, resulting in inefficiency.
One example of this would be an officer from Houston, Texas visits Dallas, Texas on vacation. During his trip, he witnesses a gas station being robbed. Since he is sworn in the state of Texas, he is required to do something to hinder or stop the felony crime. If he pulls his gun (which hopefully he is carrying off-duty just for situations like this) and orders the suspect to the ground and then dials 9-1-1 on his cell phone. The suspect may begin to resist at that point, resulting in the officer dropping his phone: if he's yelling "I need cover, code 3, at Loaf N Jug, north 32nd and Carefree Circle," into the phone on the ground, there's a chance that the operator may have no idea what "cover, code 3" means. Simple english would be a much more effective form of communication in a situation like this.
AAS Criminal Justice, BS Public Administration, 2 years law enforcement.