Many efforts are underway to promote data sharing in psychology, however it is currently unclear if the in-principle benefits of data availability are being realized in practice. In a recent study, we found that a mandatory open data policy introduced at the journal Cognition led to a substantial increase in available data, but a considerable portion of this data was not reusable. For data to be reusable, it needs to be clearly structured and well-documented. Open data alone will not be enough to achieve the benefits envisioned by proponents of data sharing.