Siri may be useless to some people, especially if they have easy access to a computer and are able to type questions into a search engine. For people who need answers on the go, Siri can be a useful tool. For example, Siri may be useful to someone who is driving and cannot type or write a note to themselves.
They can ask Siri to make a note and remind them later. This could also be a very useful tool for someone with a physical disability or dyslexia. They may find it easier to ask Siri a question rather than researching it on their own.