I didn't use Grunt and Prepros, but I use Gulp.
Comfortable? - mega convenient. Get used to it quickly, at least I I felt)).
Define a project structure, a template so to speak, put the plugin, prescribed tasks for each task at the end writing task which will monitor the files and run the required tasks. All. Do it once and forget, well, except that the Supplement will want new plugins. Deploy the project with one command in console - it's magic ))
PS I'm not versed in JS
Not to say it's much needed here, unless its something to write. And for the same plugin has a detailed documentation with examples.