A common usecase during change is that you don't know if the result of the change is a new revision, new variant or a new item or might be dropped. In Windchill, the user is forced to revise, then he can do a save as, but a unreleased revision will remain and pollute the revision history. As in Pro/IIntralink 3x (and other plm systems), the user was able to work on the current revision and could decide during checkin if this shall become a new revision or a new item. In this way, no unused revisions is created.