Humans can have a high or low feeling of control over their actions or their environment. But does this subjective sense of agency have a practical impact on our behaviour? Studies which investigated the impact of sense of agency on human performance came to inconsistent conclusions. While some found that sense of agency improved the ability to master cognitively demanding tasks, others found that high sense of agency was associated with lower task performance. Based on recent empirical work from our and other laboratories, we propose that these seemingly contradictory findings indicate dissociable mechanisms of agency-related influences. On the one hand, perceived controllability of the environment can enhance cognitive performance, since humans have a higher motivation to invest mental effort in tasks if they believe that the task outcome directly depends on their behaviour. On the other hand, humans often show an agency-related preference bias, meaning they automatically gravitate towards actions which they, rightly or wrongly, associate with a high degree of control. Such and agency-related bias can lead to irrational or suboptimal behaviour, since humans might gravitate to a less beneficial behaviour simply because it is associated with a higher subjective feeling of control. We will discuss the factors that determine if sense of agency is more likely to be beneficial or detrimental to goal-directed performance. Determining how sense of agency can both support and undermine goal-directed behaviour will be crucial to understand the functional role of sense of agency for human cognition.