When I needed to use an agent, I used to use Qantas Travel until they shut down. Then I went to Flight Center (better then some of the other travel agent options in North Canberra). It really depends on which agent you deal with. I've had some shocking agents and some really good ones.
The current agent I deal with is so popular that she only takes appointments.
Some of the others I've dealt with wouldn't know 1100 from 2300.
When I went to the nearest Flight Center branch last year to book a DAS13 and extra short flights for the connecting DONE3, she was quite surprised and impressed that I had everything (flights, availability, required fare classes, etc) all ready and she just had to enter them into their system and get the price.
There have been times when I've found better flights for my parents holidays then their agent has. A few years ago, before they found their current agent, they were on a RTW trip and were traveling DUB-JFK. Their agent wanted to send them back via AMS. Mum doesn't like flying and refuses to spend more then 8 hours in a plane at a time such that their trip last year to southern Europe routed CBR-MEL-KUL-DXB-FCO out and DXB-BKK-SYD on the way back with stops in DXB and south east Asia (until they started booking Business...), so you can imange her response to the agent when I looked up the airlines and available flights for their RTW and told them there was a non stop direct DUB-JFK flight valid for their RTW ticket.