How do travel agents generally work?

This may be a dumb question, but I consider myself very good at planning trips, doing research, finding the best "bang for buck", creating itineraries, etc.. My fiancé & I are in the process of booking the first leg of our Asia honeymoon to the Maldives, and are truly overwhelmed by the number of resort options! How does working with a travel agency or consultant work? Are they costly? Are we likely to find lower rates? Are we likely to miss out on any upgrades or honeymoon experiences from the resort if we don't book direct? Thanks in advance 🙂