Agile values clean code; waterfall may but doesn't have to

Agile and Waterfall are different in a number of ways.

Agile promises that your code is always ready to ship. Waterfall promises that the code will be ready on a specific date in the future.

Agile promises that your system passes the tests (at least the tests for code that has been implemented). Waterfall promises that every requested feature will be implemented.

There is another difference between Agile and Waterfall. Agile values clean code; Waterfall values code that performs as intended but has no notion of code quality. The Agile cycle includes a step for refactoring, a time for developers to modify the code and improve its design. The Waterfall method has no corresponding step or phase.

Which is not to say that Waterfall projects always result in poorly designed code. It is possible to build well-designed code with Waterfall. Agile explicitly recognizes the value of clean code and allocates time for correcting design errors. Waterfall, in contrast, has its multiple phases (analysis, design, coding, testing, and deployment) with the assumption that working code is clean code -- or code of acceptable quality.

I have seen (and participated in) a number of Waterfall projects, and the prevailing attitude is that code improvements can always be made later, "as time allows". The problem is that time never allows.

Many project managers have the mindset that developers should be working on features with "business value". Typically these changes fall into one of three categories: feature to increase revenue, features to reduce costs, and defect corrections. The mindset also considers any effort outside of those areas to be not adding value to the business and therefore not worthy of attention.

Improving code quality is an investment in the future. It is positioning the code to handle changes -- in requirements or staff or technology -- and reducing the effort and cost of those changes. In this light, Agile is looking to the future, and waterfall is looking to the past (or perhaps only the current release).