From my experience the main differences are that the add-in enables automatic processing of emails into context lists, assignment to projects, deferring into calander, filing, creating waiting for lists etc. - much of which can be achieved by manual settings (except I think the project bit). I use the add-in and find that it required little set up by me and just works so the less time I have to spend configuring and messing around with outlook the happier I am - just my view