I knew my comment would be a bit spicy for HN :-) Frankly, I'm skeptical that it actually was significant for them. IMO people grossly overestimate the utility

I knew my comment would be a bit spicy for HN :-) Frankly, I'm skeptical that it actually was significant for them. IMO people grossly overestimate the utility of a 10% or even 20% increase in speed. (A 90% increase is probably worth the effort, while 50% is borderline.) If a user clicks on a button and it feels slow (e.g. 500ms), then it's still going to feel slow if you speed it up but it's still the same order of magnitude (e.g. 400ms). Roughly the same is true at all different levels e.g. if you speed things up from 5 hours to 4 hours then it's still long enough that it shapes your day. A similar point applies to hardware costs. And it's even more true if there's some absolute ceiling e.g. if you speed up your service by 20% so it doesn't overflow then you'll still be close to danger if conditions perturb slightly. And all the above is not even relevant to the article. It's talking about how to preallocate a list. There's no point doing that unless you then populate the list! In most situations that's going to dwarf the time to create the list object, and at the very least is likely to match it. So you're likely to be talking about a tiny fraction of an overall runtime.