In Javascript, what is the motivation or advantage of using var foo = function foo(i) { ... } ?

Question

I see that in the answer of

http://stackoverflow.com/questions/3233582/in-javascript-why-write-var-querystringtohash-function-querystringtohash-qu

which is doing something like

var foo = function foo(param) {
  ...
}

in that particular case, why do that instead of just using

function foo(param) {
  ...
}

? What is the advantage or motivation of doing that?