I would never trust and agent with things like Fastpass pass reservations, ADRs, etc. Have read horror stories her on the DIS of people whose travel agents basically held FP/ADR reservations "hostage" and we're unresponsive to requests to make changes. And the TA wouldn't give the password to their clients so they could make their own changes.
I would never give that kind of control to someone!
Now this boggles me. I don't know how a TA can hold ADRs hostage and the only think I think they could do to met up your Fast passes would be to cancel the trip altogether.
When I work with a client who knows Disney and wants to do all of the ADR and FP themselves, I just book the hotel and Magic Express and be there to offer advice and answer questions. %They are in total control of their ADR and FP.
When I have a client who wants me to book ADR and FP, I either book the ADRs under their name and provide them with the reservation number to link or I have them provide me their
MDE account name and password and then I book it all directly under MDE so that it is linked.
BUT, they still have total control over it. And if I did go psycho on them and change the password, they can reset it easily by sending a password reset request the their email, thereby locking ME out.
I handle FP by either going into their MDE or, if they are not comfortable with then, they make me a "family and Friend" and I can then book their FP.
So, the only thing I have exclusive control over is their actual hotel reservation