Don't learn a new syntax as with preprocessors such LESS or SASS. You write css and you get css, and if you stop using stylecow or change to other css processor your code will remain valid.
Vendor prefixes, old flexbox syntax, old webkit gradient, rem values, opacity, resolution media queries, pseudoselectors, etc. Don't spend your time fixing, but creating.
Variables, nested rules, custom media, custom selectors, color manipulation, extend, calc, flexbox, etc. All using the w3c syntax. See all available plugins.
There are two styles (normal and minify) but you can create your own code style. Do you prefer spaces or tabs, simple or double quotes, 0.5em or .5em?
No need to search and install dozens of packages and care about the correct order or the plugins (like POSTCSS). There's no plugin conflicts, just install and use.
The stylecow.json file contains all your settings (browser support, plugins to use, code format, etc). You can run it by CLI, grunt, gulp, webpack or jsTransformer.
A watcher stylecow -w and a browser live reload stylecow -r are included. Enought for simple use cases, if you don't want to install additional packages like browser-sync.