Nice work. I’d like to add another point that, while being obvious, is often missed by people. Take time to understand the functionality as it stands and talk to users or stakeholders as to what their understanding is of how it should function (vs how it currently functions). Without this knowledge we can’t make sure our quick fix works well (and makes things better) and we certainly can’t undertake an extensive re-write.

We also need to remember that in the rewrite/heavy refactor scenario we effectively have to reconstruct the business case for the functionality and need a set of requirements to validate the new output against.