> doable technical challenge with clear requirements

That's a Project Management issue, not an implementation concern.

In my case, there was no requirement that said "use 16-bit long division." However, we had committed to a particular processor family (MC68HC05), and the calculation precision required 16-bit math. IIRC, there was a compiler available, but it cost more than the rest of the project and the code it produced wouldn't have fit into the variant of the processor that I was using anyway.

The actual requirement would have looked more like "detect a 0.1% decrease in signal that persists for 10 seconds, then do X."