I use a travel agent depending on the cost of the trip--no point in them booking EZ LGW_PRG for instanmce but long haul things can be very different.
She got me a fare £1000 less on VS to ORD than anything on the net by using a bit of fancy footwork (well finger work really) around a two night hotel stay which I didn't use and the fact that VS had some special promotional fares only available to agents when the route restarted for the summer.
The business has certainly changed but a proper travel professional can really help save money or add value in another way such as routing or hotel stays.