I know of a TEE being done for ablations, but in my (limited) experience it happens concurrent with the procedure. As the ablation is being done, each burn, the tip of the RF wand is placed against tissue and held there for a few seconds...depending on the energy being applied and how deeply the EP wants to destroy tissue below the endothelium. This is where the danger lies: the phrenic nerve and the esophagus both pass close to the area being cauterized, and nobody, but nobody, wants to damage those items. So, the TEE, placed down the esophagus, and with its ultrasound tip held at the same height as the left atrium, they monitor the placement of the RF tip to ensure it isn't going to burn those two.
I have never heard of a TEE administered prior to an ablation, but it's conceivable that the EP wants a pre-established situation of your heart, how much it is rotated compared to others, the separation of the pulmonary veins perhaps...just wild guessing. Maybe exactly where your nerve and esophagus are in relation to the areas about to be lesioned.......? The point is, if the EP wants it, it must be because she/he wants to ensure both your safety and his/her success....no repeats, please! The imaging provided is going to be important, and I would not be able to argue against it.