Qassams and Grads are not precision aimed devices. If you get them to go in a general direction, you are doing good. They carry only a small amount of explosives. If they do any damage at all, it is usually more from the impact than from the explosive. Having said that, the Qassam will fall somewhere, whether it is intercepted or not. It can still be dangerous, even if intercepted. In fact, it may do more damage if intercepted due to the larger amount of junk falling from the sky. It is an interesting side note that the first casualties from a Qassam in a very long time occurred after Iron Dome was deployed.
Syria foreign minister in Tehran for talks with Iran, Russia (Reuters)
from the article: Israel deploys third Iron Dome anti-rocket battery near Ashdod