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Are there any major benefits of using Sass over postCSS?
Honestly, we have no beef with the postCSS team, but if you checkout their marketing, they definitely aren't fans of ours!
postCSS is great for prefixing and other last-second optimizations... in fact, I use it with Sass in most of my projects. They can do some stuff we just can't (or don't think we should) do magically with an actual language like Sass.
And yeah, you can use postCSS with enough addons and magical features to make it pretty much look and act like Sass, but the downside is that you've built an entirely non-standard sub-language yourself.
One thing that we really pride ourselves on in the Sass-team is that we really think through every single language feature we add. Natalie, the lead designer of the language, is extremely picky about what goes in. We consider all angles of how a feature would affect our user base now, and with respect to what the W3C is planning in the future. It's a lot more complex than you'd think!
So, I use Sass still, because I want some more powerful language features but I also want to make sure that the next maintainer of the project will have a standard understanding of the code. And, I know how strict we are with ensuring that we do right by our users with stability and predictability.
The big thing that keeps bringing me back to Sass is that it's batteries included. When a codebase is using Sass I immediately know which features are available to me. With postCSS offloading it's features to plugins, I need to know which plugins are being used in a project.
Additionally in a plugin based world there are ongoing costs like handling plugin upgrades, and dealing with plugins that get abandoned.
Batteries included solutions like Sass let me focus on my code.