Certain types of projects can have very similar pieces and may make good templates for other projects. For example, if you have shows that go up in your facility that have certain general steps, such as "Build Set", "Move In Set", "Hand Lights", "Rehearsals", etc., you can make a project that is a template that includes the groups and typical tasks associated with a project of this type. This can then be used as a template that is duplicated, along with all tasks and task participants.
You may also want to duplicate a projects like "2011 Auction", or "2010 Dinner Fundraiser".
When you duplicate a project, you use a wizard with a series of screens where you can make a variety of decisions to indicate how you want to make changes to the original project when creating the duplicate of the project.