Explain why we do what we do.
Well, if unit tests and acceptance tests were enough, we wouldn't bother. But as your application grows in size and complexity, the likelihood of bugs also grows. Functional tests help ensure that new features don't break old ones, and that your site doesn't start behaving in unexpected ways when the codebase changes.
Fluid 960 Grid System, created by Stephen Bau, based on the 960 Grid System by Nathan Smith. Released under the GPL/ MIT Licenses.