It’s a pretty fundamental aspect of radio operation that you shouldn’t push the “transmit” button unless you actually intend to transmit. But you’d be surprised how often someone “sits on the microphone” on the net frequency! The resulting open carrier ties up the net, preventing any communication from taking place. Even coordinating a change to a secondary net frequency becomes impossible.
Of course we all know enough not to jam the net on purpose. But accidents happen. The microphone may get stuck under a clipboard, or wedged between a seat and another part of the car, in such a way to push the transmit button. So when you put down your mic, be extra careful about where you put it. Don’t be “that guy (or gal)”!