This is useful when we want to use a past version as a starting point for new changes.
To see how the Multiple Check-Out Model behaves compared to the exclusive check-out model, we will go through the same set of changes and observe the differences between the two models. In order to do that we need to start from the same file version we started with when using the Exclusive Check-Out Model. Hence, we need to undo the changes and revert back to the starting version.
We could, of course, manually change the file to be the same as the starting version, but we can use the built-in functionality in SourceSafe to do just that.
There are two approaches to undo version changes depending on the history we need to keep: