I often find myself (re)factoring when beginning work if the codebase is not in the shape (design rather than quality) that it needs to be in for the particular

I often find myself (re)factoring when beginning work if the codebase is not in the shape (design rather than quality) that it needs to be in for the particular new features to fit well within it. The reason I wouldn't factor after implementation is that it should have followed a design that already identified the factors that are being separated. Whenever there's continuous refactoring, the factors aren't so much known and decided at a high level, it's typically more an exercise of deduplication. If you can't name the thing (or why) you're factoring it's blind deduplication, which still has some value but is much lower. If someone says they want to refactor, I'll ask what's the factor and why. A system separated along well chosen seams allows things to naturally and easily fit in its design.