Earlier quoted context omitted.
Any system that is capable of emitting any data, can emit bytes from print debugging. Could be log file, socket, or even pulses along a GPIO pin. If the system can't emit any data, well, you're kind of stuck anyway.
Pulses on a GPIO pin are not print statements. A huge proportion of computing devices have no method of producing any out put, other than to some form of actuator, at all. "print statements" are useless in this class of device. Stretching the definition of "print statement" to recording pulses from a pin is, well, a stretch! Poor young programmers. If the only tool you have is a hemmer, every problem is a thumb.
Yes, they are. How do you think text terminals work?