Unfortunately not all kinds of slowness only happen in hotspots. This is true for CPU cycles, but if an occasional task uses all memory, it's going to mess up everything downstream as well.

Like, unrolling a `for` loop that only has 5 iterations makes sense. But if you have 100 iterations, then the larger memory footprint of all the code might actually make it slower than just keeping the `for` loop.

In some cases, you can use Duff's Device. https://en.wikipedia.org/wiki/Duff%27s_device

I disagree. Programmers may care about performance, but project managers certainly don't and they always have the final say.

LOL no. Offer a dev choice between a framework that is trending on Twitter, vs one that is 100x faster but "legacy" (meaning more than a year old) and she'll choose the first one every time, and the project manager won't know the difference, or care if he did.

When I take an hour to profile and analyze some request and say “I think we can cut this thing’s response time by 80% by optimizing $X, which will result in an overall page load time reduction of 3s”, that’s way easier to sell than “I want to figure out why this page load is so slow” and then reporting back a week later with “shrug I optimized 5 things and it didn’t get faster. Dunno.”