Some version control tools don't let you create local, private versions. That is too bad. That doesn't mean that doing so is not a version control concern.

Even when using a version control system that allows for robust local branches, sometimes it is nice to be able to revert a specific file's state to a known recent version that you never bothered to commit. Sometimes editor undo is sufficient for this, sometimes not. Dropbox and Google Drive have both saved me some time in this area (like 15-30 minutes, not days, but even that is appreciated) recently.