Reason #3 to use Teams is Co-Authoring/Document Collaboration. They mean the same thing. Have you heard these terms thrown around in relation to Teams? Although the features has been around since 2013 - using the feature within Teams brings it a whole new meaning and ease of functionality.
Co-Authoring or document collaboration is when 2 or more people are working on a document simultaneously in Real-Time! It's an amazing collaborative tool that is most often and most effectively used within Teams. Although you CAN collaborate in real-time - you don't have to and you can still take advantage of the great collaboration of this feature.
This feature is one of the reasons that takes Teams to the next level as more than a virtual conferencing tool for Microsoft Office (O365) users. This type of virtual collaboration allows users to edit an office document with other users.