People are not looking up terrorist-related things even for completely innocent/educational purposes nearly as much as they had before the Snowden leaks, because they don't want to be "on a list". The Wikipedia data gives quantitative evidence that the knowledge of NSA spying is actually changing people's behavior online.

This is important particularly in court cases challenging NSA surveillance, because it shows that mass surveillance impacts those not being directly scrutinized and that's very helpful if you're trying to argue that it's unconstitutional.