The reason for this policy is because All Editors are Equal, and you must not assume that new editors are vandals, or that you know better than them. For example, if a user empties a page, you should assume it was an accident or test rather than a deliberate act of vandalism. You can correct the edit, and ask the user to be more careful next time, and even show them where the Sandbox is. You should not tell off or shout at the user. Remember to be patient with newcomers. They may not know how to edit a wiki or what's supposed to be added as content.