To be precise, in every case where the environment only cares about your actions and not what algorithm you use to produce them, any algorithm that can be improved by randomization can always be improved further by derandomization.
Consider the heads-tails-edge game. Betting on edge is a deterministic strategy with a low payoff. It can be improved on by randomisation: randomly betting on heads with p=0.5 and tails with p=0.5 is a stochastic strategy which offers improved returns—and there is no deterministic strategy which produces superior results to it.
Consider the heads-tails-edge game. Betting on edge is a deterministic strategy with a low payoff. It can be improved on by randomisation: randomly betting on heads with p=0.5 and tails with p=0.5 is a stochastic strategy which offers improved returns—and there is no deterministic strategy which produces superior results to it.