Project versions are copies of projects that allow you to save snapshots of project data at different points in time. Project versions are mandatory for Milestone Trend Analysis (MTA), which is a tool that allows you to monitor and compare the planned and actual dates of milestones in a project over time. Project versions can be created automaticallybased on user status, which means that you can define rules that trigger the creation of project versions when certain user statuses are set for project objects. Reference:https://help.sap.com/doc/0f069b2e08b748f1b480d4c8b46c3c49/100/en-US/6a7a9f0a6e421014e10000000a174cb4.html