Greenfielding when there's already existing code to do what you want adds bloat and allows for regressions. Using previously-developed frameworks for e.g. valid

Greenfielding when there's already existing code to do what you want adds bloat and allows for regressions. Using previously-developed frameworks for e.g. validation, can help reduce bloat, and can help ensure the codebase is maintainable for the long run. Think about it: do you want to have 5 separately-implemented code paths that all accomplish essentially the same thing, or one generic codepath that handles all the reasonable cases?