By feeding the output of the camera to the laptop you can see what the camera is seeing in real time if you can't be behind the camera. You can position the laptop where you can see it's screen, then you can press the remote shutter release at exactly the right moment to capture the shot you are after.
Most useful, if, like the photographer in this case, you are working alone.
NOTE: You don't have to have software on the laptop to actually control the camera as you can use a remote for the camera.
How you view the image will depend on your camera. The term you need to search for is "tethering".