First, Apple is reusing the R&D that it's done for the iPhone, rather than sticking with the old-style bezel or coming up with some in-display camera setup.
Secondly, it offers more screen area without having to make the whole laptop huge.
In fact, you're getting a 16.2-inch display in a package only marginally bigger than the 15-inch MacBook Pro -- 14.01 inches (35.57 cm) x 9.77 inches (24.81 cm) x 0.66 inch (1.68 cm) vs 13.75 inches (34.93 cm) x 9.48 inches (24.07 cm) x 0.61 inch (1.55 cm).
Then there's branding.
Apple's already embracing it. It did the same with the iPhone.
I'm willing to bet a steak dinner that a year from now, there will be a lot of notched laptops out there.
It's an ingenious yet simple solution to the problem of putting a camera into a laptop display while keeping the bezel to a minimum.