CSS is an incredible technology. However, some key features are just plain missing. You might not even realize you need some of these features until you use SASS/SCSS. Sass adds useful color functions (lighten, darken, etc), allows you to nest selectors, and use variables and mixins. It adds these features seamlessly over the top of CSS, meaning you can add Sass to a project and rename all of your .css files to .scss! This thin layer of extension makes it, in my eyes, the perfect CSS technology. I have used Sass in every single project I have made since I first used it, and I will likely continue to use it in every single project I make in the future.
"Sass is the most mature, stable, and powerful professional grade CSS extension language in the world."