The rollback extension allows a user to revert all of the edits by one user on a page to the last edit by a different user. This feature should only be used in reverting edits that are clearly vandalism, and any possibly good faith edits should be reverted with the undo button. This is done so that the user reverting can explain why they are reverting the edit, for the benefit of both the original editor and any other users looking through the article's history; using rollback suggests that the user vandalised, hence no edit summary is needed.