As an Israeli, I've always heard the Iron Dome rockets are stupid expensive to fire, so the IDF really only wants to fire them during scenarios that are high risk -- e.g., a rocket fired toward the Negev is much lower priority than a rocket fired at Tel Aviv.
On another note, I think that as programmers it's an interesting exercise to speculate as to the nature of the computer systems Iron Dome employs in order to mitigate attacks. AFAIK, Iron Dome rockets are only fired when high-value areas are targeted or there is a high probability of success. Can you imagine the kinds of online learning models we employ nowadays, being able to evaluate a set of inputs in <10s ? Even a complex Bayesian inference algorithm that could solve for a probable strike area in that short time with reasonable accuracy is incredible.
As colloquial evidence, a family member of mine recently posted a photo of Iron Dome intercepting a rocket almost directly over his home. So maybe it's not that accurate or that effective, but when it does work it's worth almost every dollar or shekel spent.