Suppose you are collaborating with someone outside the Tabbles network. You send a tagged document to him by email; he modifies the document and sends it back to you by email (or by Dropbox, or in general from the internet). In this case, the new document that you receive will have preserved the tags of the original. i.e. you won’t have to tag it again. This is possible because Tabbles embeds the tags in the files themselves, so when they are modified and sent across the internet, tags are not lost.
(This feature is only available for Microsoft Office documents).