In addition to sibling replies, function keys are very useful in debuggers (to step in/over, set breakpoints, ...). And lots of other things that don't immediately come to mind.

I'm old enough to remember WordPerfect on DOS, with a paper template to put over the function keys on your keyboard as a little cheat sheet for all their functions.

Yeah, when I’ve had to break down and reach for a debugger, it was gdb. I’m sure there are shortcuts but since it was a rare event, I just typed “step” and “continue” like a caveman, haha.