Consciousness has causal powers
Consciousness has utility in creatures with complex nervous systems insofar as it loads the dice in favour of their survival. Hence, consciousness has causal powers.
If consciousness serves some utility—such that an organism with consciousness is better off than an organism without it—then consciousness will serve some function. Consciousness can only serve a function for an organism if consciousness has effects—ie that it's capable of causing change. To have effects, consciousness must have causal powers.
William James (1879).