You can view the files from multiple Google accounts and Google Apps accounts, so the add-on is a good option to virtually merge your accounts. Since the plug-in doesn't offer all the features available in Google Docs, you'll still need to open the online interface to publish a document, to use gadgets in Google Spreadsheets or to collaborate with other users. While you can manage the collaborators in Microsoft Office, you can't collaborate in real-time and your changes will overwrite the changes made by your collaborators.
Despite its name, OffiSync doesn't actually sync Google Docs with your computer and it doesn't even show the most current version of a document, assuming that other people edited it after you opened the document in Microsoft Office.
It could be an option for those who aren't comfortable with using an online office application, but they want to backup the documents online. It's probably not a good idea to use it this way since Google Docs doesn't have all the features that are available in Microsoft Office and the documents won't look the same. In its current incarnation, the plug-in isn't very useful for those who use the collaboration features from Google Docs.
Here are some potential uses:
* create a document in Microsoft Word and quickly import it in Google Docs, without using the online interface
* open a document created in Google Docs to improve the layout before printing it
* use some functions from Microsoft Excel that aren't available in Google Spreadsheets