A site survey is a structured walk-through of the flight location BEFORE the drone is even powered up: where the obstacles and wires are, where people can appear from, where the pilot will stand, where the sun sits, and which way an emergency landing would go.
It is a named professional procedure, and it is done on the ground while there is still no time pressure. In the air there are no spare seconds left for any of these answers — so they are prepared in advance.