I know a lot of people thinks that preprocessors take a lot of time consuming but you're missing a lot of points.
First of all, if you're some type of decent developer you're going to minify your CSS so you'll have to install Gulp or Grunt anyway.
Second, you just need to configure it just once it might take an hour to configure it if you haven't used any preprocessors before but thats it.
And Third, some preprocessors take longer to configure like SASS or SCSS but if you use Stylus you just literally have to install Node, and NPM stylus and you can run a watcher that already comes with stylus and that's it. Like 15min tops and is only once that you have to install it (globally in your computer).
It saves a lot of time, could be hours or days at the end of a project, so saying that it is a waste of time to configure it is just stupid. And if you're still thinking that you can download PREPROS that does all of that and you can use prefixer, minify, etc without installing anything extra.