When you need to manage one web-server (or AS) there isn't problems. because you make all operations just one time. But what about next situation: you have several servers and need to do the same operations several times? Of course, you can repeat your set of commands several times. However there is much better solution - Capistrano. In fact, it was developed in Ruby and for Ruby projects need. Don't worry, you can use it not for only Ruby applications:)
Capistrano uses special DSL for specifying commands.
Yeap, it's perfect solution for executing commands in parallel