That's really interesting. So the point is that they're effectively the same in the sense of the amount of work necessary to write the code, and putting in the effort to code the first one might be premature optimisation if running f1() thousands of times isn't actually an issue, or that you might need to debounce f1(), or guard against side effects, which is 'harder'.

I think I'd find it really hard to let go of the idea that my code might be doing something wasteful like calling a function it doesn't really need to call. Maybe it's because I've been coding since the early 90s when clock cycles and memory actually mattered a bit more. It's certainly given me something to think about. Thanks.