A Product Owner must release each Increment when it makes sense to release it. The timing of the release should be based on the value that the Increment brings to the stakeholders and the readiness of the product for use. This decision should be strategically aligned to maximize the product's impact, which means considering factors such as market conditions, user needs, and business objectives. Therefore, the Product Owner should release the Increment when it delivers the most value, not strictly at the end of every Sprint or only when it is defect-free.