ClearCase is a version file system masquerading as project version control. It's heavyweight, clumsy, and brittle, and it's easy to get yourself in an inconsistent state.
At one enterprise in my past it could take months to merge for release, during which time the entire repository was locked for everyone. I suspect it was the 30 years of commit history. It took years to move to something more modern.
Much better than Microsoft [Visual] SourceSafe.
