For those that have the time and don't mind the hours it takes to put it all together then yes you can do it yourself. Personally I travel a lot for work and really do not have the time to dedicate to it as it needs. The time I am at home is quality time with my husband and children. I love that I can be outside playing with my children while my TA handles all the details. My time is precious and have very little of it that isn't work related. The more of it I can spend with my family the better
Also since
ABD is only by phone I don't have the time to sit there and be on hold.
I can't even begin to count the amount of money my TA has saved me by applying discounts when they became available. There is no way that I would have been able to keep up with it especially since a lot of times I was in a conference or on a plane and not able to be on the phone holding to take care of it myself. Since she has been so valuable to me even the few times that I do have the time I still let her take care of the details. I don't want to take the work away from her on the very few occassions I can do it myself. I have built up a great relationship with her and that started right at the first vacation she handled for me
To the original poster - it really comes down to what you prefer. Do you like the planning and having the time to take care of all the little details? If not then a good TA is invaluable, at least to me.
As the others have said, in this economy it is nice to be able to give someone work which doesn't actually cost you a cent out of your pocket