JSS is makes a lot of sense when styling React components and styled-components is a really nice implementation of JSS. I still get to write pure CSS, but in a more componentized way. With CSS post-processors like SASS and LESS, you spend a lot of time deciding where your .scss or .less files belong, which classes should be shared, and generally fighting the component nature of React. With styled-components, you get the best of CSS and React. In this project, I have ZERO CSS files or global CSS classes and I leverage mixins quite a bit.