By definition history is a chronological record of significant events (as affecting a nation or institution) often including an explanation of their causes.
Because everything and everyone has history - we decided to create history in our application.
The question is: Where and why we added history?
The answer: We added history in the Issues tab for a very simple reason: In order to anticipate the future you must know the history.
Issues History can be reached in Issues Options in Issues tab. To check the history for a specific issue you should open the issue and click on the History tab. Then, details for every change that was made to an issue is shown: the action that was performed, project, task, priority, status, type, severity, assigned to and description of the issue.
Soon to come are the histories for: Projects&Tasks, Time&Expenses and Wikis.