PostCSS is a framework to create a CSS tools. Preprocessors (Sass/Less) is only one type of tools that you could build on top of PostCSS.
So using PostCSS != not using Sass. You could use Sass for processors, but still using PostCSS for other CSS tools types — for Autoprefixer, Stylelint, cssnano.
So using PostCSS != not using Sass. You could use Sass for processors, but still using PostCSS for other CSS tools types — for Autoprefixer, Stylelint, cssnano.