[lambda]

For one, it means that you don't need to have a precompiler step in the development process. You can more easily edit the value inline in your browser's developer tools. You can more easily put together simple static sites.

Another is that you can use it in conjunction with calc(), which you can't do in a preprocessor. Take a look at some example use cases for calc, which can't be done in a preprocessor: http://css-tricks.com/a-couple-of-use-cases-for-calc/ Now instead of just using constant values in those, you can use variables. This can be even more powerful for responsive designs, because you can set the variable to different values based on a media query.