Assuming "fast enough for a good user experience", expecially early on in a product lifecycle, I prefer to focus on development speed than product speed.
I get your point. This is an outlier, but hear me out:
For some of the workloads I run on https://workers.dev, I can tell you that going from 100ms to 10ms is something I look for every single day. I am also very interested in anything that takes the memory usage down into KBs from high MBs, say.
In 2020, a webpage that "only" takes 10 seconds to load is a miracle of performance and user-friendliness. Load times of up to a minute are the new normal.
I'm pretty sure dismissive comments such as yours lead us to this bad place.
Of course by "load" I don't mean TTFB, I mean actually loading the full page, including all the spinners, reflows, banners and toolbars popping into your page, images, etc.
If you go from 10sec to 1 sec, absolutely.
If you go from 1sec to 100ms, maybe.
If you go from 100ms to 10ms, unlikely.
Assuming "fast enough for a good user experience", expecially early on in a product lifecycle, I prefer to focus on development speed than product speed.