I was trying to book a flight from Chicago->Seoul, and the options showed at least $2000 for the cheapest flight, which involved a 33hr total journey through China and Japan. I then asked my Korean friends, who recommended a travel agent and they got me a $1700 ticket with only 17hrs direct flight
The best part is they can put me on a wait list for cheap tickets!
Most travel agents on long-distance, well travelled routes work through consolidators. These consolidators buy tickets (or promise to buy tickets) in bulk far in advance, and then re-sell them later. This is what I've heard about segments like USA <-> India.
Funny, I've always had the opposite experience: every time I've used a travel agent, they always found more expensive flights with worse timings (time of day, layover, etc), and I end up requesting specific flights based on what I've found online.