Reports should behave more like objects than what they do. They should be like Lifecycle Templates or Workflow Templates in how they act from an administration standpoint. They should have check out and check in. They should be versioned so that one can go back to an earlier version if needed.
Scenerio 1: Reports are working in 10.2 but system is upgraded to 11.0. Reports get "Upgraded" at somepoint after the upgrade and no longer work correctly. Admin starts tinkering with report and saves not knowing that it was upgraded and that upgraded reports cannot be undone once saved after upgrade. So now there is no way to go back to a working "version". Undo would have worked before a save was initiated.
Scenerio 2: When creating a new report or modifying an existing one and trying multiple things and sometimes a wrong path is taken. Would be beneficial to restore to a point that is known instead of trying to undo what was done.