I could see just powering through because modern hardware is fast enough to do so being an option.

Adding 20% to a 10 second operation is a lot longer on a wall clock than adding 20% to a 1 second operation.

I'm not a Hurd contributor ( or any OS kernel / library ).

I'm not sure this holds today. One example I can see is related to crypto. We used to have specific hardware for computing cryptography functions but it's now handled directly in standard hardware and the software has not evolved ( but it's been faster and faster to compute checksum functions )