All to give you that classic camera-operator-wasn't-ready kind of feel.
The idea is that you apply it to a locked down shot to make it look a bit messy. And since you're doing it in post, you can play with it as much as you like. I find that very appealing, because making something look naturally accidental can be very difficult and time consuming. So why not do it in post?
And it's $49, which isn't too bad. My only gripe; it's only for Final Cut Pro X, and even though I have Final Cut Pro X it's not my editing tool of choice at the moment.
Of course, you could recreate the effects yourself using After Effects or Motion, but a plug-in will save you some time.