I know someone who spent about three months on a 10-line fix, which was primarily a configuration tweak. As part of that process, they had to discover and describe emergent properties of an architecture that formed organically over several years from multiple teams building components that interacted with one another in non-trivial ways. They ended up getting a promotion due to that code’s incredible impact.

Still, I'd very much write the reasoning down in the commit log. My commit logs sometimes were essay-long