It's per user, which cover any "extra" eligible assignments. As for assigning the license, Microsoft does not enforce licensing requirements in code for many of its products. Which of course doesn't mean you can use the feature "for free", you are still required to have sufficient licenses provisioned in the tenant.
I'd still recommend assigning the license, as other features might depend on it, and at some point Microsoft might start enforcing it for services that didn't check for license assignment previously.