Strategically, terror tactics have been a waste of time and money. Bombing, of civilian populations, as a means to frighten a nation into capitulating, as opposed to infrastructure damage, did not work, at all, during WW II, despite estimated civilian deaths of over 20 millions.
All the terror tactics, in the past two decades, including the WTC towers in 2001, have been like tiny pin pricks in the fabric of Western society. The worst real damage that we have suffered, as a society, is that we have to take our shoes off before boarding an airplane.
Terror tactics, as presently practiced, is a benefit only as propaganda to try to keep funds and volunteers coming into a given terror group, whether it be a group like Al Qaeda or ISIL, or the Republican Party in the U.S..