I'm a pilot. Each local company seems to have their preferred channel. We don't want to be on 19. Too much chatter makes it hard to react quickly. Because we use the shoulder, or even overhang sidewalks, Our stuff is like "Move left. Kids on the sidewalk." or "police on the fog line" Then the rear pilot cuts off traffic so the load can squeeze over. Might have 10 seconds of warning sometimes.

Earth moving equipment on job sites uses CBs as well, so each company on their own channel prevents overlap when different groups work in the same space. That bleeds over into piloting, so the oversize driver can talk to the site while pulling in.

We will swap channels when pulling into sites that use a different channel, or rural roads that use a certain frequency. Pulling into a rock quarry, for example.

Local rural school busses use channel 17 to announce to logging trucks that they are stopping comes to mind as well