Hello,
the notificiation emails are about changes to any document in a site that you are a member of and potentially changes performed by users that you follow (subscriptions). There is no way in standard Alfresco to subscribe only to changes made on an individual document. That is one reason why we developed a commercial notification addon which allows users to subscribe to individual folder hierarchies or individual documents while also providing user choice about which events they want to be notified about (e.g. all changes or just specific versioning events).
Regards
Axel