Back in 1990 or so I worked at a networking company (Vitalink) that was using whatever source control was popular back then. I forget which one, but the important thing was that rather than allowing multiple check outs followed by resolve, that system would lock a file when it was opened for edit and nobody else could make edits until the file was checked in.

One young developer checked out a couple files to "clean them up" with some refactoring. But because he changed some function interfaces, he needed to check out the files which called those functions. And since he was editing those files he decided to refactor them too. Pretty quickly he had more than half the files locked and everyone was beating on him for doing that. But because he had so many partial edits in progress and things weren't yet compiling and running, he prevented a dozen other people from doing much work for a few days.