> if you’re writing CSS professionally then there’s really no good excuse for not using a CSS preprocessor.

CSS preprocessors aren't without their own problems as well. An app that I'm currently working on has a history of semantic HTML, but having no room for compromise had resulted in a CSS file that is 4000 lines long.

There were lots of cases where an innocent looking @extend created monster selectors (https://twitter.com/mezzoblue/status/390274599167877120/phot...). This is non-obvious behaviour that should be avoided.