The question is fair, so answer it properly

Anyone can book a flight. Pretending otherwise loses the room. What a booking site cannot do is judgment, and judgment is what people pay for once a trip is complicated enough or expensive enough to be worth getting right.

Knowing what not to book

A site shows you everything that matches your filters. An advisor tells you the connection is too tight, the hotel is being renovated, the crossing is rough that month and the tour you are looking at is a coach tour in everything but name.

Being reachable when it goes wrong

A canceled flight at midnight is where the value shows up. A phone number that answers is worth more than the margin on the booking.

Access and perks that are not public

Preferred partner status buys room upgrades, credits and amenities that do not appear on any public rate. Clients notice these, and they are the reason a trip booked through an advisor can cost the same and be better.