It's commonly used when you pick up a radio on a public band.
So if you have a jobsite where there are 100 radios, and someone needs to reach Ted, they'll page the radio and say something like "Hey Ted, do you copy?" and Ted will respond with "Go for Ted," which means yes, Ted is here and he's listening, go ahead.
It was used in a small way some 40 years ago and never really caught on.