[JS] Currying with Javascript

I first read about the term curry in the book "Javascript: The Good Parts" by Douglas Crockford. According to the author, currying allows us to create a new function by combining a function and some arguments. The example in the book was something along the following line.

function addBase(base) {
  return function(num) {
    return num + base;
  };
}

var add2 = addBase(2);
add2(6); // => 8

When I first read about it, I thought it was a cool thing to show off with your friends about your coding skills. Nevertherless, I didn't find currying to be very useful. But after a few times seeing it being used in different repos, I just realize how powerful it is as a tool to generate function and simplify callback.