As a TA, I can tell you that using a TA's services can be of great value! We take care of all of the details (including ADRs) and at no extra cost to you. We will also automatically rebook your package when special rates are announced. Plus, we can add a litlle bit of extra magic to your trip that you wouldn't be able to do if you booked on your own.
As others have mentioned, you really do want to find a TA that is a Disney Specialist.