Why use a task runner?
In one word: automation. The less work you have to do when performing repetitive tasks like minification, compilation, unit testing, linting, etc, the easier your job becomes. After you've configured it, a task runner can do most of that mundane work for you—and your team—with basically zero effort.
Why use Grunt?
The Grunt ecosystem is huge and it's growing every day. With literally hundreds of plugins to choose from, you can use Grunt to automate just about anything with a minimum of effort. If someone hasn't already built what you need, authoring and publishing your own Grunt plugin to npm is a breeze.
Available Grunt plugins
Many of the tasks you need are already available as Grunt Plugins, and new plugins are published every day. While the plugin listing is more complete, here's a few you may have heard of.
Here's a preview!
While installing grunt is simple, it's slightly more involved to get it running on your project. To see what your effort will win you, take a look at this example output from running Grunt in a sample project.
grunt Running "jshint:gruntfile" (jshint) task >> 1 file lint free. Running "jshint:src" (jshint) task >> 1 file lint free. Running "jshint:test" (jshint) task >> 1 file lint free. Running "qunit:files" (qunit) task Testing test/tiny-pubsub.html....OK >> 4 assertions passed (23ms) Running "clean:files" (clean) task Cleaning "dist"...OK Running "concat:dist" (concat) task File "dist/ba-tiny-pubsub.js" created. Running "uglify:dist" (uglify) task File "dist/ba-tiny-pubsub.min.js" created. Uncompressed size: 389 bytes. Compressed size: 119 bytes gzipped (185 bytes minified). Done, without errors.
Who uses Grunt?
These are just a few companies and projects that are using Grunt. See more here.