I have used travel agents some of the times; made my own bookings some other times and delegated the travel arrangements to the company's secretary yet other times.
My experiences are mixed. Best experiences were with the company secretaries who had fun arranging trips; I prefer to book simple trips myself (if it can be done in 15 minutes on the Internet...), but in more complex cases it is good to have someone who is willing to spend the 30 minutes on hold arranging things with airlines... even if it costs some $s
Biggest issue with an agent is that it requires time to explain all the requirements and preferences; things like "find the ticket that is cheapest if we have two changes in flight dates"...
I have had no complaints about the service from the agent I've used; but seen little value, considering that I can book on the Internet without paying their fee.