Currently in confluence, there is no way to ensure that users enter comments to describe the purpose of their page edits. This dilutes the value of the page history. Our organization, and I'm sure many others, would like the option of making these page-edit comments mandatory unless the edit is marked as a "Minor change". This would require users to add comments and simultaneously encourage them to use the "Minor change" checkbox when appropriate, thus reducing the amount of unnecessary notification emails and RSS.
I've marked this issue as Priority: Major due to the fact that it is a loss of potential functionality and that there exists no easy workaround (that I know of) to enable this kind of validation.