If you get a good TA and don't mind them having to be the one to make any changes to your reservations and handle payments, then it isn't a problem. The downside is if you get a bad TA, it can be difficult to cut them off, and they can botch stuff. Examples of things I've heard TAs have botched that are hard to reverse are misspelling a name on a reservation such that it doesn't match the travel documents at check in, not being responsive timely to customer requests, failing to make payments on time resulting in missed payment deadlines and the reservation getting dropped by Disney, not adequately communicating to clients restrictions around certain special rates (e.g. *GT), and just generally giving advice that may be good for one family but horrible for another (e.g., recommending an aft-facing room because of the big balconies, only to have the family be miserable because of aft vibrations and smoke, which bother some people more than others).