I hope to never have to push Sass and CSS to these types of limits manually like Twitter did with their heart animation. But if you follow along with how they did it, it's brilliant and I'm sure you'll learn something new worth speaking to in the future.
A common-sense, visual explanation.
As Andrey says out of the gate, PostCSS being 1.5x faster won't make much of a difference to your day-to-day tasks. However, benchmarking your code and knowing what it's actually doing from version to version is a worthy takeaway.
Static site generators aren't going anywhere!