If you want to identify and segregate relevant data and preserve them for a long term for legal purpose, then you can convert a review set case to a legal hold case.
From the navigation pane, go to Activate.
The Activate page appears.
Click Case manager.
The Case manager page appears.
In the Name column, click the case to convert to a legal hold case.
The case page appears.
In the upper-right area of the page, click Convert to legal hold.
A message appears confirming the request.