Although the ability to track changes over document versions is really helpful in some situations, it also creates unnecessary noise or confusion in other cases.  For example, the author maybe making a lot of small changes over say a few days including word smithing, formatting, or content changes.  These are captured as new document versions and changes.  The author may not want the reviewers and readers to see all these changes and just wants to present the current state as the "new starting point document" for collaboration or reference.  He may want to also expand the number of readers of the document at this time and they also don't need to see the minute detail of all the changes since the origination.

Allowing the author to delete some or all of the versions or changes tracked may also help with the tension between "personal workspace edits" versus public workspace actions.  I have in the past created some edits elsewhere before "pasting" back into Buzzword so that not all of my "live" edits had to be kept with the history of the document changes.