What is Israel Doing?

Israel has bombed pretty much every route out of Beruit now. Why now? Why not before? What exactly are they hoping to achieve here? Taking out infrastructure like this is only useful if you exploit the opportunities it presents, and I have seen nothing to indicate this is the case yet. So what exactly do the Israelis think they are doing? What is their game plan? I am starting to think they are playing this by ear, and botching it.