The model is fairly similar to CVS, which also keeps histories of files instead of a history of the repository. The ability to have half of your repository come from one "branch" and the other half from a different branch is actually seen as a feature. This enables workflows similar to what you can do with submodules in git.

Having to manage your config specs and the inability to go back to old versions of your software (or in fact just have something reproducible for your build servers) unless you meticulously label everything makes Clearcase of course barely useable. It gets extra interesting if you use multi-site Clearcase and your replicas stop synching.