I'll give one example. I was on a status run SYD>MEL>AKL and then returning the next day AKL>BNE>SYD. I had Intentionally chosen the A330 flight for the AKL>BNE.
As I was boarding in MEL, I was contacted by MR and advised the AKL>BNE flight had been cancelled, and Qantas by default were rebooking me onto another BNE>AKL flight later in the day (or maybe even the next day, I can't recall). Mind you at this time nothing had been received by QF, either by email, or in the app to advise of the cancellation and changes.
MR gave me the option to go with the Qantas offerings, or just to take a direct AKL>SYD flight, and then sent me all the screenshots from the booking system I'd need to raise an email with QF for requesting original routing credits. All taken care of by the travel agent, no extra cost, nothing on my side other than raising the ORC request.
There is definitely value in using a competent TA.