Well, it performs the usual function of calling somebody "fascist"--serving as a term of insult and disgust.
More broadly, I think nothing is gained, analytically. Fascism is:
* A strong belief that--through social darwinism--morality is ultimately tied to blood and race, understood as descent and genetic relationship. * A strong rejection of the "liberal" belief that individuals have rights that any legitimate state is bound to respect * In its place, an assertion that individuals have duties to the state, seen as the decision-making organ of the collectivity. * A strong fear of Marxist communism, and an eagerness to use all weapons to combat it.
Al-Qaeda doesn't fit the pattern. I think the analogy with Cromwell's Puritans is much closer, a la Walzer's _Revolution of the Saints_...
Brad DeLong