Related but not the same model of computer.

If the computer has visibility of the program counter using LED's (right next to the switches) visually the operator can see what the program is doing.

Well, at least they have an idea. "It's flushing the line printer. See, how the left most PC leds are off, and the pattern being displayed. it is writing data to the printer".

Or, "something is wrong, the PC is stuck in a loop, see the pattern".

Very different way to get a feel for an operating program.

small, oft ran program, of course.