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I work in embedded systems. Right now, my organization has two full-time programmers and two occasional programmers. It's rare that the same project is worked on by two programmers. All code is stored on a network drive. There are folders for the current production code, another folder for the source for every released version throughout history, and a third folder for active work. We have an automated system (Mercurial being abused) that makes backups of every changed code file in Working every fifteen minutes, so we can revert to previous states.
My question is this: is it worth the trouble to set up a formal versioning system in an environment like this? Why or why not?