Over the life of a report, it can go through various modifications/tweaks. It would be nice if the reporting object had the ability to allow a person with update access to track the type of modification being made.
We are trying to maintain this information outside of the report on a Task, but it would be so much easier it you could just include an update about what change you are making in the actual report so it would be visible to anyone else that had manage access to the report.