I sometimes book through a corporate TA and sometimes do it myself.

Pros for the TA: Cashflow since I don't have to fund it (even temporarily). Also, they seem to be able to get a credit for a non-refundable ticket - so if I think I may have to cancel, I'll book through them.

Pros for doing it myself: UuA possibilities (since the TA is in another country - this seems to preclude UuA), OnBusiness points and Avios/spend from using the BA Amex card.

That said, I rarely seem to get UuA chances even when I buy the ticket - my hit rate is less than 25% and I'll easily hit the 2-4-1 threshold so it's pretty marginal really.