GUI Debuggers
Back in the dark ages of computing before we had powerful GUI debuggers to allow us to step through code and inspect it, a time honoured technique to debug code was to put statements in the code to print to standard out.
i.e. printf statements.
See the C sandbox for an example.
Compared to sprinkling one’s code with printf statements and then having to remove them all when it was time to ship the product, graphical debuggers seem like a large improvement.