This a common question that we get as luxury travel agents and there is solid list of reasons why the wealthiest people in the world have an appetite for this service.

Nizuc Resort and Spa, Cancun, Mexico
Reason #1: It Saves Time
Once you've established rapport with your agent they know your preferences. If you want to do a trip throughout Italy, they'll be able to rattle off all of the hotels that fit your dream vacation. A lot of people prefer to just text their agent dates, location and budget, knowing that the agent will curate a list of desirable stops. This is preferred over spending hours sifting through often misleading marketing materials, stressing over whether to book now or later and worrying about negotiating with or communicating to hotels ahead of time.
For big spenders an added benefit is the guest profile, maintained by the travel advisor, which can automatically communicate preferences to a hotel (i.e. Fiji water in the room, a chilled bottle of a specific alcohol or self-parking near the valet for super cars).
For group bookings and corporate travel, weeks of planning can be saved, especially during the bidding process as travel agents have access to resources that allow them to get bids from all hotels with a click of a button. This is much easier than reaching out to 50 hotels individually and trying to keep track of all responses.

Mount Nelson, a Belmond Hotel, Cape Town, South Africa
Reason #2: It Saves Money
Agents have access to rates that are not open to the general public. While some deals can be found on sites like Expedia, travel agent rates will typically beat the price or add value to beat the deal through extra benefits.
For big spenders, like those spending $5,000 - $45,000 a night in five-star hotels, a travel agent can negotiate in ways that even savvy travelers could not. Personal relationships with General Managers and higher ups in hotel brands, paired with volume driven by a luxury agency means a better deal for VIPs.
For group bookings and corporate travel, agents often negotiate dozens of deals with the properties per year, making it easier (and quicker) to get to the real numbers. When in-house team members or typical leisure travelers attempt to negotiate a room block, they are often out of their element and may think 20% is a great deal. Your travel agent will know better and the hotel will know that the travel agent expects more.

Splendido Mare, a Belmond Hotel, Portofino, Italy
Reason #3: More Benefits
Beyond special rates, agent also have access to special benefits programs which often include:
Free Early/Late Check-in and Check-out
Breakfast for two every day
$100 resort credit
Upgrade Based on Availability (we've seen people get upgraded 2-3 room categories)
Amenities upon arrival
A more high touch experience with hotel staff (because they don't want to tarnish their relationships with major benefits programs)

Mahali Mzuri, Motorogi Conservancy Masai Mara, Kenya
Reason #4: Better Service From the Hotel
If you book on a major travel discount site the hotel will usually be less inclined to go above and beyond for you. Sites like Expedia charge large marketing fees to the hotels, making your stay less profitable. Being less profitable means you are less important. Even if one of these major sites offered an upgrade based on availability, your upgrade status would be lower priority than a client who used a travel agent.

Monasterio, a Belmond Hotel, Cusco, Peru
Reason #5: Your Travel Agent Has Your Back if Something Goes Wrong
Hotels, Airlines and other vendors can sometimes try to pull the wool over the eyes of travelers, especially when a problem arises. Should an unexpected bump in the road occur on your trip, you simply text your travel agent. You do not have to wait on hold with an airline when your flight gets canceled or argue with staff at a hotel desk, your agent will smooth things over so you can continue on in vacation mode.

Trump Hotel, Downtown Chicago, USA
Reason #6: Using a Deep Red Travel Agent is Free
This is the reason 99% of people stick with good agents once they've found them; they get all of the benefits above with ZERO additional expense. Most agents charge fees, however, Deep Red Travel agents and all agents in the LuxRally Travel Network do not and cannot charge fees to their clients (or they will get kicked out of the network). How do Deep Red Travel agents get paid? By the vendors. Vendors pay a commission to all agents and the commission amount is more than enough to make a client worth the agent's time. You could think about it like a marketing budget set aside for all guests and clients that a vendor considers in their budgets. This is why a hotel will treat agent referred clients better than big travel website clients, the commission / marketing cost is much lower and therefore the profitability is higher, making the travel agent guest more desirable as a repeat client.
When we could not get a room at the Sanctuary Resort in Kiawah Island, not only did Deep Red Travel get us a room.. they got us an Oceanfront Room at an incredible rate! DRT was easy to work with and Very responsive.. will definitely use again!