Here are the upsides and downsides I have experienced from our corporate travel agents.

Downsides:

* Even though I give them dates, flight numbers, etc. they still mess up 9 out of 10 bookings.
* We have to pay them £26 per person per itinerary. On top of the airlines published price (i.e. ba.com price).
* I can't upgrade until I get to the airport.
* I have to fight them every time to book WTP because it is outside the travel policy. Even though nobody in accounting bats an eyelid as I asked them the proper way to bypass the policy as I always need the WTP luggage allowance. (yes I know I get the same in Y as a gold but they don't need to know that).
* Getting them to change a booking is impossible (we have already paid their fee and there is nothing in it for them). I have always just booked another flight instead.

Upsides:

* The rebate from the airlines pays for the board to go to Tahiti every year. (hence not using the corporate agent is virtually sackable)

On the plus side the agents I usually end up speaking to now all know that I know more about flying than them. They no longer tell me I am wrong when I ask for one PNR for me and a colleague on ET or AA Y so we both get an extra luggage allowance from my gold card. Also they have finally learnt the IATA airport codes for where I usually fly!

I am getting away with refusing to use the agent for car hire, probably since our special corporate rate with National is about double what avisba charges me, but with National it is for class A verses class C with avisba! Even when avisba charged me 109 euros for a single day rental in Paris.