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.
Grunt is a tool in the Build Automation category of a tech stack.
What are some alternatives to Grunt?
npm is the command-line interface to the npm ecosystem. It is battle-tested, surprisingly flexible, and used by hundreds of thousands of JavaScript developers every day.
Visual Studio is a suite of component-based software development tools and other technologies for building powerful, high-performance applications.
Out of the box, IntelliJ IDEA provides a comprehensive feature set including tools and integrations with the most important modern technologies and frameworks for enterprise and web development with Java, Scala, Groovy and other languages.
A bundler for javascript and friends. Packs many modules into a few bundled assets. Code Splitting allows to load parts for the application on demand. Through "loaders" modules can be CommonJs, AMD, ES6 modules, CSS, Images, JSON, Coffeescript, LESS, ... and your custom stuff.
Yeoman, Lineman, Aerobatic, BrowserSync, Babel and 7 more are some of the popular tools that integrate with Grunt. Here's a list of all 12 tools that integrate with Grunt.