I've tried css-dryer, which is similar in concept to server side LESS and SASS. I found it to be problematic on a large project because even though the CSS was compact in its source form, what actually got compiled ended up getting huge. It was slow to download and inefficient for the browser to process. The brevity of the source language ended up being an invitation to use CSS in a style was extremely verbose upon compilation. It also added operational complexity to have to deal with compiling the css. For example we wanted to use CSS in some of our javascript tests and then we had to deal with running the dryer from the test server. We eventually ripped it out at fairly great cost and went back to vanilla css, where it was clear to everyone what everything meant and we didn't have to worry about a huge inflation of the code. Maybe there's something smarter about these frameworks that avoids these issues?