It is plain that an individual's being conscious and an individual's being conscious of various things are both crucial for successful functioning. But it is far less clear how, if at all, it is also useful for a person's psychological states to occur consciously, as against those states occurring but without being conscious. Restricting attention to cognitive and desiderative states, a number of suggestions are current about how the consciousness of those states may be useful. It has been held that such consciousness enhances processes of rational thought and planning, intentional action, executive function, and the correction of complex reasoning. I examine these and related proposals in the light of various empirical findings and theoretical considerations and conclude that the consciousness of cognitive and desiderative states is unlikely to be useful in these or related ways. This undermines a reliance on evolutionary selection pressures in explaining why such states so often occur consciously in humans. I propose an alternative explanation, on which cognitive and desiderative states come to be conscious as a result of other highly useful psychological developments, some involving language. But on this explanation the consciousness of these states itself adds no significant function to that of those other developments.