Well that's largely theoretical and Siri needs largely more input than is worth the trouble. It lacks context and because of Apple focus on privacy/security is largely unable to learn who you are to be able to do stuff depending on what it knows about you.
If you ask Siri about playing some music, it will go the dumb route of finding the tracks that seems to be a close linguistic match of what you said (if it correctly understood you in the first place) when in fact you may have meant another track of the same name. Which means you always need to overspecify with lots of details (like the artist and album) and that defeat the purpose of having an "assistant".
Another example would be asking it to call your father, which it will fail to do so unless you have correctly filled the contact card with a relation field linked to you. So you need to fill in all the details about everyone (and remember what name/details you used), otherwise you are stuck just relying on rigid naming like a phone book. Moderately useful and since it require upfront work the payoff potential isn't very good. If Siri would be able to figure out who's who just from the communications happening on your device, it could be better, but Apple has dug itself into a hole with their privacy marketing.
The whole point of an (human) assistant is that it knows you, your behaviors, how you think, what you like. So he/she can help you with less effort on your part because you don't have to overspecify every details that would be obvious to you and anyone who knows you well enough.
Siri is hopeless because it doesn't really know you, it only use some very simple heuristic to try to be useful. One example is how it always offer to give me the route home when I turn on the car, even when I'm only running errands and the next stop is just another shop. It is not only unhelpful but annoying because giving me the route home when I'm only a few kilometers away is not particularly useful in the first place.