Corporately we work with a TA. The greatest benefit is time savings. I can tell my TA approximately when I want to travel and where I'm going and she does all the leg work of figuring out flights, etc. They track my hotel preferences, rental car preferences as well and so when I get my itinerary back, everything is set up without the hassle of doing it myself. And, personally, if it were just 1 trip a week or a month, I would handle it myself but I'm often on complicated schedules that have me in 3-5 different cities a week and it's just easier to farm that out to someone else and allow me to focus on what needs to get done.