CVS is something that you will use when you would like to track the differences and changes that you have made on the file. The SVN can be used when you would like to check all of the revisions that have been made. You will use SVN when you would like to track the changes that you have made to a certain project especially if the changes that have been made are crucial to the whole project.
If you would like to do file migration, it is also recommended that you will make use of SVN as compared to CVN because SVN will be able to serve its purpose properly.