The maximum possible entropy is in a sense sampled by users various passwords. The sampling can be biased, so rules can technically eliminate such biases and le

The maximum possible entropy is in a sense sampled by users various passwords. The sampling can be biased, so rules can technically eliminate such biases and lead to higher effective entropy. Furthermore, there is a benefit in forcing the user to not share the same password across multiple websites which can be achieved by imposing extra (or ideally mutually exclusive) password rules. Of course I am just playing devils advocate here.