In the "old days" people were used to the locked checkout scheme, and we were afraid of merges. In a large code base most people were working on different files

In the "old days" people were used to the locked checkout scheme, and we were afraid of merges. In a large code base most people were working on different files, so lock conflicts ("I want to edit a file but somebody else has it checked out") were fairly rare. We used SCCS on a shared filesystem. If you really needed to edit a file somebody else had locked, you simply removed the lock file. Of course, social convention was that you better have a really good reason for doing that. If you went on vacation with files locked, it was pretty much expected that your locks would be removed, and that you'd have to merge or otherwise deal with your stranded edits.