Guard helps you to automate tedious, repetitive tasks in you everyday development. I guess that the most common tasks Guard is used for is to fire of all kind of tests (rspec, testunit, minutest, cucumber, jasmine), generates assets (haml, sass, coffeescript, less, compass, sprockets, jammit), manage other servers/services (spork, rails, pow, spin, delayed jobs, resque, unicorn) and update the browser with live reload. This are just a few examples, there are many plugins available, just search RubyGems
https://rubygems.org/search?utf8=%E2%9C%93&query=guard- and find a Guard plugin that manages a task you do manually.