The frameworks are great for mocking sites up: instead of modifying CSS for every layout you test the framework gives you a few classes with sane defaults that

The frameworks are great for mocking sites up: instead of modifying CSS for every layout you test the framework gives you a few classes with sane defaults that you can easily switch between to align and re-align your columns. My typical workflow is to include a stylesheet that defines a basic grid and use that when working on the design. Towards deployment I write the grid to my main stylesheet using the elements' proper class-names and ids.