Whether slow code matters or not depends on the scale, because executing code requires power. If it's a one off or otherwise rarely executed, yeah, it doesn't

Whether slow code matters or not depends on the scale, because executing code requires power. If it's a one off or otherwise rarely executed, yeah, it doesn't matter much. But it starts to matter when it's constantly running on a significant number of systems. Widely distributed frequently running slow code can waste a lot of energy. Cell phones and laptops heat up and have a shorter battery life. Even desktops require more power. On the global scale, a large number of such systems can waste several nuclear reactors worth of electricity. 10 times slower code might require 10 times the number of servers. Maybe it doesn't matter much when it's just the difference between one and 10 servers. Or perhaps you don't even consume 10% of a single server. But there's a point when the hardware and power costs start to dominate. The scale matters.