Imagine that you have a function that expects a reference to a function. Here is an example of such a function:
function bar(fn) { fn(); }
Now imagine that the function that you want to pass to bar accepts a parameter. Here is an example of such a function:
function foo(arg) { alert(arg); }
With the help of a closure this is no problem:
bar(function e() { foo('hello'); });
PS: Kudos go to Weirdan for providing the solution to this problem.