Your example really clicked with me, having written a substantial quantity of JS in a "memory managed" way to avoid GC, and avoiding memcpy by passing buffers in place of pointers.

My initial instinct is that putting such considerations behind a preprocessor syntax has the disadvantage of making them more opaque and magic, and that I personally would continue to do such things more explicitly - which I realise is an ironic thing to say about an untyped, interpreted language, it's probably just the little pseudo "grey beard" on my shoulder which occasionally whispers silly things about "building their own computer out of rocks and twigs".

I guess the point is that there's a balance to the cost vs benefit: making it more convenient (what you call ergonomics), making it more accessible to those that were less likely to manually use that technique, and perhaps resulting in an average of more performant code; but at the cost of more obscurity, and more "magic", perhaps resulting in less educated programmers.

I'm probably overthinking it. Ultimately this argument even applies to for loops, but it's worth being conscious of that cost - it's likely a good idea.