What is Grunt for?

I'm trying to get into Grunt, which I am new to, but I do not understand its utility.

I understand that it is a taskrunner. I understand that it can be used to do things like bundle, uglify, jshint, minify, etc etc etc, anything that can be turned into a scripted task.

But I don't see what advantage this gives, since nearly all of these can be run from the command line anyway, which is to say you could just combine them using a simple shell script. It seems to me that setting up grunt + gruntfiles and writing tasks is more work than writing a shell script, rather than less.

Could someone help me to understand what I'm missing about this?

(Not sure if this should be an SO question instead of Programmers.SE, please advise.)