The main purpose of a project backlog in agile practices is to serve as a prioritized list of work items or features that need to be completed. It acts as a central repository of tasks that are continuously refined and prioritized through team collaboration. The backlog ensures that the development team focuses on the most valuable work, allowing for adaptability and quicker responses to changing requirements. Regularly reviewing and updating the backlog promotes transparency, helps in planning sprints, and aligns the team with stakeholder expectations, ultimately enhancing project delivery.