Whenever you run ‘svn commit’ on a particular file or folder, the working copy ends up with a mix of revisions, because the item you’ve just committed is at the HEAD revision, while the other items are at the previous revision.The working copy will continue to contain mixed revisions, until you run ‘svn update’ and bring the entire working copy to the same revision.
Tagging Mixed Revisions Although it’s possible to copy the file revisions in a working copy to create a tag, it is good practice to use repository URLs – this is especially true when your working copy contains mixed revisions.
The bad news is that it's very easy to drift strategy is that by the time you're finished with your branch, it may be near-impossible to merge your changes back into the trunk without a huge number of conflicts.
Instead, you and Sally might continue to share changes as you work.
Working in big enterprise company, you have to justify before moving from one version control tool to another.
But why should I replace Subversion with Git or Mercurial.